You might also want to talk with A-Shed in Denver. They are completely local and offer custom buildout with windows, etc. Free in home consultation. http://a-shed.com/
I have a great contractor referral for you if you'd like to get in touch with me as well...
Good luck! Art = happy!
I would start with estimates from Home Depot and Lowes and also check with Tuffshed. If that does not meed your needs you will need to check with a building contractor. The cost could vary from $10,000 to $20,000 easily depending on how extensive you want to make it. I have seen these outbuildings made that look just like the home. If that is the case it could get quite expensive in Greenwood Village. Good Idea though. I would check with zoning and with your HOA before making any major plans. Good success with your project.
Robert McGuire ASR
Your Castle Real Estate
Direct - 303-669-1246
My advice to you would be to check with the city before you even start getting bids, if you haven't already. I know here in Arvada whether or not we were allowed to build was based on a percentage of un-built-upon lot space.