So I need help on making a custom class. I want to be a Small Guns user, wear Power Armor, do lots of damage, and have a good chance of getting critical hits. Could someone tell me the Skills, perks, etc,to create this build?

Well if you want to be a sniper and it sounds like you do...

ST: 5
PE: 7
EN: 3
CH: 1
IN: 6
AG: 9
LK: 9

Perks:

Level 3: Awareness
Level 6: Sharpshooter
Level 9: Bonus Rate of Fire
Level 12: Better Criticals (can be taken earlier)
Level 15: More Criticals

By this point you need to have become a member of the Brotherhood of Steel and got the surgery to increase perception. So with Perception at 8.

Level 18: Sniper

Tag Skills: Small Guns, Speech and Outdoorsen.

Traits: If you want to give up being able to carry 50 LBS you can pick small frame and have one extra point to put into your special (your agility goes up by one). If you do, take the extra point out of agility and put it in luck giving you a luck of 10 which is best for critical hits. Or you can put it into Perception, that way you can put off going to Lost Hills and paying money to boost your Perception. You will need PE of 8 to get the sniper perk. But keep in mind you will only be able to carry 100 LBS but your armour class will be 9.
If you want to give up the amount of damage you do in favour of more criticals, go with Finesse.

Other then those two options I wouldn't pick any traits besides Bloody Mess.

Whatever you do don't pick Fast Shot.

When you get to Lost Hills and you need to in order to get power armour, you can get surgeries to increase your agility, strength, endurance as well as your perception by one, but they cost alot of caps.

Seeing how charisma is meaningless in FO1 you may as well give charisma 1 and follow Styles build but bump agi to 9 or 10.

I can't remember if there is an agility implant in FO1, if there is, agility 9. If there isn't, give yourself agi 10.

That should give you 3? shots with most weapons with bonus rof. With eye shots that is generally three kills a turn.

Finesse is great trait for any who desires crits. You may also consider trying to go luck 10.

Is it completely meaningless? I don't believe I have ever played Fallout with Charisma lower then three. I am not saying you are wrong, just want to know how it is useless.

Doesn't it effect how some characters react to you? Like if you have really low Charisma some people will not even talk with you?

Nope. Useless. Only changes starting skills but since you can overcome that easily with tagging them or just investing skill points it's a dump stat.

Ok good to know. (After all these years and countless play throughs, I am still learning stuff )

So OP do what myself and evlbastrd said and you will have an awesome sniper character

I just finished editing my character creation post.