I've recently started to look around for a bigger home, also with the intention of commandeering a room for a dedicated home-theater setup. (sound treated, stepped seating, projector, etc.)

What are the best qualities to look for in a room like this? Are there certain shapes, sizes or surfaces that are best? What's a good height? Are there certain traits to avoid at all costs?

I know some of you have built rooms like this for yourselves and I'm wondering if you've learned what some of the tips or pitfalls of this sort of space might be.