[@TimeMasterX] The Watchtower sits atop the LexCorp building like this:

[center][img]https://upload.wikimedia.org/wikipedia/en/f/f2/Stark_Tower.jpg[/img][/center]
Regarding what's inside, I'd suggest you don't over-think things too much. A big circular table where the Justice League sit and the usual base nonsense. Try not to get too caught up in the specifics.