I'm doing the "happy dance" for you! My wonderful DH did this for me last year. It ended up being 14' X 24', and believe me, you will appreciate that extra 4 ft. It took us almost a year to finish it up, but I'm so happy with it. I've posted extensively about it:
http://www.quiltingboard.com/main-f1...2-t103882.html
There is also an "Update on Quilting Shed" that I'm having trouble finding. Just let me know if you have any questions that I can help you with. We put ours not too far from our back door and our neighbor, who is a carpenter, built us a deck between them which we will enjoy having year-around. DH requested a recliner out in my shed so he could "hang out" with me when he got lonesome!