Few things to note about dragon PCs.
1) As PCs (or cohorts), you are expected to use the same stat generation method as the rest of your players (be it rolling or point buy) and allow them access to gear as a PC. If you ran the dragon right out of the MM, this means its stats would be way weaker than it should be. With 28 point buy, you would be shortchanging the dragon of roughly 4 points in str/dex/con/int (more with gear). 
2) Dragon PCs aren't really formidable in combat, their usefulness lies in their other abilities like skills, movement modes, flight, senses and alternate breath weapons. They will be slaughtered in straight melee, which is why I suggested tricking out its breath weapon. Yes, this does risk making it a 1-trick pony, but at least it should be an effective one. 
Here is a small excerpt regarding a friend's experiences with a dragon cohort.
[Sblock]The silver dragon in my campaign is actually an NPC, a cohort of the PC  wizard. She started off as his dragon familiar (using the Dragon  Familiar feat) and then became his dragon cohort (using the Dragon  Cohort feat). So she started pretty weak and has slowly caught up to the  rest of the party (at least to the other party members; the wizard  actually has pulled ahead because his player does so much roleplaying  and storyline stuff). The wizard's player has been very paranoid about  exposing her to danger. She usually flies by and breathes with Maximize  Breath. Only now is he realizing that she's turned into a tank, with by  far the best AC and the second most hit points. I think he's going to  put the 
wild special ability on her 
belt of giant strength and 
cloak of resistance.  Up until now she's been heavily overshadowed in melee by the party's  half-celestial, but I think she's starting to catch up, and will get  even better at he next level because her damage will increase with her  size. 
She's also fairly versatile, and has by far the best  assortment of skills in the party. She has 11 skills maxed out:  Appraise, Knowledge (arcana, geography, nature), Listen, Search, Sense  Motive, Spot, Swim (cross class), Tumble (cross class), and Use Magic  Device. The party has given her 
cure wands, 
magic missile wands, and even their 
staff of life.  They made a staff of revivification and mass heal and gave it to her  too. (She has clerical spells on her spell list, so she can use them  even without Use Magic Device.) So she's often played the roll of  advance scout and healer. She's frankly the only party member who  actually knows how to get to the Labyrinth where they're headed, from  her Knowledge (geography) (the NPC captain of their boat knows the way  too), and she's the one who appraises all the party's treasure. I'd say  that her role until now probably wouldn't satisfy most players, but then  if a player had actually been playing her as a PC, she'd have seen more  melee and focused much earlier on getting those wild magic items to  buff her in combat. Several party members have +5 weapons, and indeed  have had them for a while, but she's got only a 
+3 amulet of mighty fists.  If a player had been running her, she's probably have a +5 amulet by  now. If she had the +5 amulet and the +6 wild belt of giant strength,  her attack bonus would rise above 30 (at only 15 hit dice). 
I  think probably since her natural weapons (other than the bite) don't do  as much damage as the best manufactured melee weapons that she probably  wouldn't deal out quite as much damage as a melee specialist of her ECL.  When she gets to 22nd level and increases to large size, however, her  bite will do the same damage as a large greatsword (but without the 1.5x  Strength or 2x Power Attack alas), her claws will do the same damage as  medium longswords (but with only .5x Strength), her wings will do the  same damage as medium short swords, and her tail will do the same as a  medium longsword but with 1.5x Strength and 2x Power Attack. When she  gets her next feat at 24th level the tail will do damage like a medium  greatsword. Since she just took Multiattack, her secondary attack will  suffer only a -2 penalty. So they even have a benefit over iterative  attacks with a manufacture weapon (plus she needs only one magic item to  make them all magical and give them an enhancement bonus to their  attack and damage rolls).
I think that she's probably not going  to get as good in melee as the party's half-celestial  barbarian2/cleric1/ranger2/fighter4/lightning warrior8, but I think she  might do in melee as well as the party's half-celestial monk 17. She's  certainly more versatile than the monk.
She's also gotten her own 1st-level spells now. We gave her 
guiding light  to help the party's archer because the wizard's player has seen her  mostly as an auxiliary, not a main combatant, having trouble seeing her  as having grown well beyond his small-sized familiar. We did give her  true strike, however, so that gives her a benefit that the  half-celestial combat specialists in the campaign don't have.
Her  big weakness, of course, is fire. "Dragons: color-coded for your  convenience." (Order of the Stick) 

 She has decent but not outstanding  saves. Once the wizard gets the wild ability on her cloak of resistance  and boots it from +3 to +5, she's actually going to have the  second-best Will save in the party. She has excellent ability scores:  Str, Int and Wis all 26, Cha 24, Con 22, Dex 20. Even without the cloak  she has the third-best Fort save in the party.
She has died  twice. The first time, when I think she was still a wyrmling, a group of  kobold elite scouts shot her out of the sky when she was spotting for  the party's spellcasters. The arrows knocked her unconscious, and the  fall killed her. Ever since, the wizard's player has been paranoid about  her dying again, and that's why he gave her the 
+6 bracers of armor and the 
+4 ring of protection. Her low touch AC--he has visions of her getting disintegrated--motivated him to bump her 
+4 gloves of Dexterity (useful only in her humanoid forms) into 
+6 wild gloves of Dexterity.  The second time she died, a kobold sorcerer and cronies nuked the party  with delayed-blast fireballs. The wizard died too. The dragon's  vulnerability to fire definitely played a role. I think had she not had  the vulnerability she wouldn't have died then. Oddly enough he has done  nothing to try to shore up her vulnerabilities, say, by getting her a 
ring of fire resistance or a 
ring of featherfalling. (I think though that he might have started carrying around a 
featherfall spell. 
Even the push for the 
wild  gloves, belt and cloak have come from me. He's been pretty content to  have her fly out of range of danger. One day the ship they had taken  from epic pirates got its rudder snagged. She and the half-celestial  lightning warrior went underwater to check it out. A group of dire  sharks swarmed them. The player was so afraid that she would get grabbed  and pulled into the depths to drown that he had her swim to the surface  and fly out of their reach on her first turn, leaving the  half-celestial alone underwater to fend for himself. Then about 30  sahuagin swarmed over the sides of the ship, so the rest of the party  stayed occupied trying to protect their crew from dying at the hands of  the sahuagin and effectively rendering the ship immobile, so nobody came  to the aid of the half-celestial. I think someone playing the dragon as  a PC would have had a better idea of her capabilities and might not  have had her flee, but he still thought of her as his little wyrmling.  
I started playing a red dragon hatchling at 1st level under  the Savage Species rules in the Shackled City Adventure Path. (Like so  many other campaigns, it lasted only a couple of levels.) Dragon issue  332 contained the level advancement tables for the chromatic dragons. I  think I got to 3rd level, which is where the red hatchling gets flight. I  found that at first level he did at least as well in melee as the  party's paladin, and probably better. He did decent damage and had good  hit points. We fought a grell or something like that that floated down,  grabbed one of the other PCs, and floated up out of range with him. It  was very frustrating that my dragon couldn't fly--and didn't have any  ranged attacks either at that level. (The red dragon doesn't get a  breath weapon until 10th level [7 hit dice].) It was nice when he got  flight at 3rd level. We never did encounter any cold damage, so his big  vulnerability didn't come into play. Indeed we rarely had to make any  saving throws at those levels, but he did have good bonuses. I think he  had to wear barding as a hatchling starts without any natural armor. I  think though that I put his highest or second-highest ability score in  Dexterity too.
I suspect that a dragon PC compares favorably at  very low levels, then maybe starts to sag a bit, but then later compares  favorably again.[/Sblock]
Hope it helps. Or at least makes for an entertaining read. 
