A couple more comments
Lord Pendragon said:
Okay, let's use this example to illustrate my earlier point. Say your wizard spends the 550gp to buy a spell. Say that it's Cat's Grace. Now he decides to craft himself a pair of Gloves of Dexterity +2. He spends another 2,000gp, plus 160xp, and four days of work. His final cost is 2,550gp, plus 160xp and four days labor. Compare this to the fighter, who must pay 4,000gp for the same item. This savings only gets better as the wizard levels up, because the increasing XP gap between levels means that he can craft until the cows come home, and he'll still most likely only be a level behind his companions, but have a pile of magic items to make up for that single lost level. Nice deal. Cut out the scribing costs, (and scribing time, which is another balancing factor here,) and the wizard's bonuses get even better.
A couple of extra points on this: To create this item works like follows:
Buy scroll (25*2*3) = 150
Decipher scroll = Read Magic or Spellcraft check
Learn Spell = Takes one day Spellcraft check DC 17. If you are a 3rd level wizard that has perhaps a +10 (6 ranks, +4 Int) to the roll you need a 7 or better to succeed. If you fail 30%, then you are out 150 gold and cannot try again until next level when your Spellcraft raises. (Where you have to buy the scroll again and then have a 25% of failure).
Write Spell: Takes 3 days for a 2nd level spell and costs 400 gp.
So, a total of 4 days and 550 gold to learn a 2nd level spell. (But, if you can sell your Gloves of Dexterity for Market Value, then you have more than paid for your initial investment and everything you make after that is pure profit.)
Now, when comparing your cost to make the item, you should multiply your exp cost * 5 (160*5= 800) to convert to equivalent gold. So, your effective cost to make Gloves of Dexterity is 2800 + 550 + 8 days = 3350 gold + 8 days.
But wait there is more, on page 178 of the DMG, 2nd paragraph under Caster Level states quite clearly that at 3rd level you cannot make this item. Nope, you will have to wait until you are 8th level.
Of course once you learn the spell, you can make items at 50% cost and then turn around and sell them at market value. Not in most campaigns I have seen.
Also, it is more effective to learn spells from someone else's spellbook, since you don't have to pay for the spell (if found as treasure) and if you fail you are not out any money. OTOH, this limits your spells to what you can find.
IMHO, the Craft Wand feat is the most useful. Since you can have on tap up to 50 spells that are very useful, but not ones that you would want to memorize all the time. Having a Wand of Invisibility (CL 3) gives you 50 30 minute duration Invisibility spells at your finger tips for a mere cost of 2250, 5 days, 180 exp. BTW, same cost for a Wand of Cat's Grace that you can use to enhance the whole party. (You still have to be at least 5th level to do this.)