D&D 5E [5E] Recommendations for Fighter BattleMaster Build

This is my first character so I'm still trying to figure out when certain things should be taken. My goal is to function as a Tank/DPS and I'm currently level 3. I really like the synergy of PAM and Sentinel, but I could see where taking the ASI for STR and CON might be better earlier on. I'm currently planning on getting CON to 18. Should I get it to 20 instead or swap out that 16->18 ASI with another feat? Any recommendations/suggestions are welcome.

Race: Human (Variant)
Background: Soldier
Alignment: LN

Proficient Skills: Athletics (STR), Perception (WIS), Intimidation (CHA), Survival (WIS), Medicine (WIS)

Roll: 16, 14, 13, 12, 11, 11

Attributes and feats:
Lv. 1: STR 17, DEX 12, CON 15, INT 11, WIS 13, CHA 11, Great Weapon Master
Lv. 4: STR 17, DEX 12, CON 15, INT 11, WIS 13, CHA 11, Great Weapon Master, Sentinel
Lv. 6: STR 17, DEX 12, CON 15, INT 11, WIS 13, CHA 11, Great Weapon Master, Sentinel, Polearm Master
Lv. 8: STR 18, DEX 12, CON 16, INT 11, WIS 13, CHA 11, Great Weapon Master, Sentinel, Polearm Master
Lv. 12: STR 20, DEX 12, CON 16, INT 11, WIS 13, CHA 11, Great Weapon Master, Sentinel, Polearm Master
Lv. 14: STR 20, DEX 12, CON 18, INT 11, WIS 13, CHA 11, Great Weapon Master, Sentinel, Polearm Master
Lv. 16: STR 20, DEX 12, CON 16, INT 11, WIS 14, CHA 11, Great Weapon Master, Sentinel, Polearm Master, Resilient (WIS)
Lv. 19: STR 20, DEX 12, CON 16, INT 11, WIS 14, CHA 11, Great Weapon Master, Sentinel, Polearm Master, Resilient (WIS), Alert

Fighting Style (Lv. 1): Great Weapon Fighting

Battle Master Maneuvers:
Lv. 3: Riposte, Menacing Attack, Trip Attack
Lv. 7: Precision Attack, Disarming Attack
Lv. 10: Evasive Footwork, Maneuvering Attack
Lv. 15: Goading Attack, Pushing Attack

What level do you actually expect the campaign to last to?

First, this will allow you to focus on your build, not some theoretical 20 level build. Second you can look at things like Resilient (Wis) and say "I'm barely getting any use from this - I should either take it sooner or not take it.)

I see you rolled, because those 1st level ability scores aren't possible with point buy (or standard array) with variant Human. High ability scores do give you the chance to get feats because you aren't as starved for, but waiting until 8th level for a melee character to get +4 to their attack/damage will leave you a bit behind the curve for a good chunk of time - that goes back to how long the camapign will actually last. I've seen a lot run through 10-12, and in that case you're going to be behind on chance to hit (which makes GWM also much less effective) for most of your character's lifespan. On the other hand if it's going to 20 it's not as big a deal.

BTW, you missed out. Polearm Master is much better starting feat than GWM, because at low level having two attacks consistently is quite nice. At 8th when you already have 2 attacks, the third isn't as much of a boost.

You could have made taking GWM so early more useful by mitigating some of the -5 to hit with Precision as one of your battlemaster superiority dice, if you haven't locked in your 3rd level yet I'd suggest that.

Great Weapon Fighting is the trap choice of fighting styles. +1 AC would probably have served better for a tank.

I agree with a lot of what Blue said. I would definitely round out Str and Con at level 4. Then take Sentinel and PAM at 6 and 8 in either order, then maxing Str. I wouldn't plan anymore after that because you have no idea what you're going to want from your character by the time you get anywhere near those levels, and most campaigns fizzle out by the teen levels anyway.

In hindsight, I would have done a lot of things differently, I would have taken the Defensive Style, and Heavy Armor Mastery at level 1. That would have put me starting with 18 Str from level 1. PAM at level 4 and Sentinel at 6, and max Str at 8. THEN I would have considered GWM at 12.

I would start with polearm master or sentinel instead of GWM. GWM does not help you a lot at low level. If polearm should be your thing, it is polearm mastery what you want at level 1. That 2nd reliable bonus action attack will be more useful than the bonus attack for a crit or takedown. The -5/+10 with a +3 bonus is mostly a trap option, which will probably start doing well after you rounded STR and CON at level 4. Keep in mind that rounding CON is not the most important thing though. You could instead take Heavy Armor Mastery at level 1 or 4 instead. That would help you stay in the fight longer overall.
You could also just be a mountain dwarf with STR 18 and 16 CON or a Half orc With 14 Wis, 14 Con and 18 Str. Or a Goliath. Human Variant is nice... but overrated. Darkvision helps a lot for a nonmagical character.

Fighter BattleMaster Build

I am planning to Multi-class my Paladin with 3 levels of fighter to pick up Action surge and Battle Master maneuvers

For my 6th level polearm battle master I took PAM at 1, Sentinel at 4, and Str +2 at 6, and the Defensive FS. Maneuvers: Menacing, Pushing, and Trip.

Riposte uses your reaction and PAM/Sentinel already have 2 good uses for your reaction that will trigger quite often. Riposte has a lot of contingencies: if you haven't already used your reaction, if a creature misses you, and if you hit. When creatures enter my reach for the first time and I hit on my Sentinel reaction attack, my top choice is Tripping Attack so that I'll have a chance to make attacks with advantage on my turn. If they are already in my reach, I'll use Pushing Attack to try to push them back out of my reach and have to get past my Sentinel reaction once again on their next turn. I save the Menacing Attack for creatures that are too big to push or trip. For my first maneuvers, I'm biased toward the ones that work any time you hit a creature with an attack and let you wait to see if you hit before you use them.

GWM is better early than it appears because you will kill many enemies in 1 hit and get a better bonus action attack. (Just ignore the -5/+10 part for a bit or use it if you fight zombie level ac targets)

polearm master is still likely better but the 2 feats are closer than they appear. The most important polearm master ability early is the reaction attack IMO

I like to do the ability scores increases late, because so many items increase stats it would be sad to put points into STR then at lvl 7 pick up a Gauntlets of Ogre Strength. This is even more important if you play AL since you can use treasure points to pick the best STR item for your tier. It takes up an attunement slot but in game its worth it.

Race: Human (Variant)
Background: Soldier
Alignment: LN

Proficient Skills: Athletics (STR), Perception (WIS), Intimidation (CHA), Sleight of Hand (DEX), Animal Handling (WIS)

I like Animal Handling w/ Solider because you have Land Vehicle proficiency. Sleight of Hand is just fun.

Point Buy: STR 10, DEX 14 (13+1), CON 16 (15+1), INT 10, WIS 13, CHA 12

Attributes and feats:
Lv. 1: Pole arm Master
Lv. 4: Sentinel
Lv. 6: Resilient Wisdom
Lv. 8: Great Weapon Master (take after Precision Attack)
Lv. 12: Lucky
Lv. 14: Alert (I also like Mobility)
Lv. 16: CON +2
Lv. 19: CON +2

Fighting Style (Lv. 1): Great Weapon Fighting

Battle Master Maneuvers:
Lv. 3: Riposte, Menacing Attack, Trip Attack (Yes!)
Lv. 7: Precision Attack, Pushing Attack
Lv. 10: Disarming Attack, Anything
Lv. 15: Anything

When to take GWM also depends a lot on your party. If your party either sets up a lot of advantage, or your Cleric casts Bless on you all the time, then you can take GWM at Lv. 6 or so. If not, then I'd max STR first.