I'm making maps, so I came here.

Hi.
I guess... welcome.
Also, as you mentioned, probably you should start by KOTH. It's easier to make than MvM or SD.

KoTH is a good place to start. Mostly so you get scale down and learn how to build your spawn room and learn optimisation through layout design. Your first couple maps will naturally be pretty shockingly bad unless you get lucky. The scale of size and entity work means KoTH maps are fast to produce and complete so it's great for taking what you've learnt and moving onto your next (better) project instead of trying to force a poorly designed huge map like payload down peoples throats for months when constantly going back to it to try and "fix it" because you spent so much time on it already.

map workshop if i remember correctly. if it isnt playable, usually the wip in wip thread