As a builder, I have been involved in a few (Well truth - at least a few ... man cave-like finished basements.) As a homeowner, and a dude, I have been left only dream.
In old houses, especially, the basements themselves sometimes are more cave than anything that could be, well, converted into (*monster truck voice*) ... "The Ultimate Dude HangOut...out...out..."
But a I guess, can really go anywhere. Right? An attic in some cases. In other cases, maybe the man cave is just a room. A Man Room.
Interior Designer (and friend) Tammy J. Dalton (http://www.tamaradalton.net) states, "This is a Trout." And in decorating, there is really only one way to deal something like it. ... That's right – "Stick it in the Man Room."