I'm thinking of making a copy of my BF key fob to get into his building
Do you think that it would be a good idea to do that?
Yes, that way I don't have to wait outside when his dumb ass isn't home.
Make sure he is ok with that before you do it. If he does not want you to do that, then don't do that.
I'm cool with snooping through his stuff and I don't trust him at all.
You should not make a key in order to sneak around his place. If you don't trust him, talk to him about it instead of going behind his back.