Rich R. said:
I added a room to my home for a pool table, as well as other things.
First of all, you have to decide exactly what you want from your room. If you are only interested in a pool room, I'm sure the addition can be done fairly simple and at a reasonable cost. My wife and I wanted a multi-functional room, with a pool table. We added a room of approximately 500 sq. ft. and we have an 8' pool table on one side and a table for games and/or dining on the other side. We also have a wet bar, a wood stove, a lot of windows, a stone floor and a few other little tid bits, to take advantage of solar heating. We were lucky in that our central HVAC unit was large enough to handle the addition, because of the solar considerations. Our room stretched the budget quite a bit, but, as I said, you have to decide what YOU are looking for in YOUR room.
I also highly recommend getting an architect involved to make your addition look like it belongs with the rest of the house. His/her services are worth every penny and the pay back will come when you want to sell.