[jkorp]

I"m in the early stages, but right now my man cave is in the basement junkroom I've cleaned out. At this point I'm only using a fan in the window, with my chair next to the window. This setup works well for solo smokes, but I would imagine 2 or more would be a problem.

Ideally you want a fresh air intake and and exhaust. If you don't have an intake you will pull air from the rest of the house and change the drafting in you house. If you have no gas or oil appliances in your house, this may not be a big deal. But if you do, you could create a down draft in your chimney by sucking the houses air out with no intake to replace.

The trick for me, when and if I ever get around to it, will be running the intake and exaust from different places. I would either have to run straight up and out the roof

I would think that you would want to keep the room apart from the house's HVAC.

Air proofing will be using weather striping around doors, styrofoam under outlet covers and probably plenty of caulk. Perhaps even plastic sheeting behind the wall material. Having the intake and exaust right will go along way to keep the smoke flowing out instead of back in.