I’m going to be starting a game with 2 other friends and I’m trying to find a good multiplayer build. one is playing a reaper and the other is a battle mage. im open to playing anything just want something that will mesh well. also im on version 1.1.9.0
There are so many things you can play, and even in multiplayer, just having a competent, self-sufficient build is good enough.
That said, it’s nice to have non-overlapping AoE buffs if you’re playing with dedicated friends. I’ll list out a few class combos that don’t overlap with your friends’ classes:
Purifier (Demolitionist + Inquisitor). The most popular gunner class. Dagallon’s set is fun for endgame as well.
Conjurer (Occultist + Shaman). Possibly the most popular class. Largely because it’s the best pet class, but it’s also a solid vitality damage caster with the Dark One set which is target-farmable, which is great if it’s one of your first characters.
Sentinel (Occultist + Oathkeeper). Solid class for retaliation builds, can also go vitality, acid, or even physical. Retaliation will be pretty tanky and the rest will probably be squishy casters, in general.
Those are three very good classes on their own and don’t overlap with your buddies. If you want something that really helps out your friends, I’d suggest running something with Shaman. The Mogdrogen’s Pact line is really strong defensively and it’s an AoE buff, plus you get Wendigo Totem for AoE heals. You can run basically any class with Shaman and it’ll be fine, it’s a very versatile and solid mastery.
If you have a particular playstyle you want to go for, I could get more specific. Hopefully that helps though!
Welcome to the forum. 
If you want to play a support type build then have a look here