Room Design for Best sound?

I am about to build an outside room. It will be a sunroom/study and my main audio room.
It will be about 18' x 22'.
So long as I get good light I can do whatever I want.

I would really appreciate any info on design, materials, etc. Is there a good book? Web site?

Any thoughts/advice are most welcome.

Here's an article that you must read...

Positive Feedback magazine writer Michael Lavigne just built a state of the art dedicated listening room(30'x21'x11') in his barn. He had Rives Audio do the design work.

His article Building a Reference Grade Listening Room is fascinating and extremely informative. Mike actually hangs out around here sometimes and posts under his name as a moniker "Mikelavigne". Try shooting him an email for more info.

Also, Rives Audio sponsors a Room Acoustics Forum on Audio Asylum that offers a wealth of information. The forum is not just for Rives products, many pros from other companies and acoustics experts hang out there offering lots of DIY advice/info. Post a question over there and you will get suggestions for a ton of acoustic design & theory books.
I'd recommend Robert Harley's "The Complete Guide to High-End Audio". It has a section on "The Room", treatments and speaker placement that is very informative and helpful.
Obviously, we hope that you will want to work with a design group like ours, but even if you don't we are very happy that you are paying attention to the room. It's for this reason we've spent a huge amount of time putting together a resource section with many articles, simulators, and tutorials. So, if you don't use a group to help with the design, then do a lot of research and reading. One of the best books is Alton Everests, Master Handbook of Acoustics. It is a great overview on the subject and touches on just about all facets of small room acoustics.

Rives Resource Page