I found your plans last summer and loved the design so I decided to build one for my wife for her birthday last August. I didn't get started until the weekend of her birthday in late August so there was little expectation to have it finished before winter. It is now 14 months later and I only have a few trim pieces left to install. We live in a harsh climate and I wanted to be able to use it through the winter so I made a few changes. I built a 2 x 12 base and insulated it with R40 and the bottom walls are 2 x 6 instead of 2 x 4 and are insulated with R20. I used twin wall polycarbonate instead of the corrugated lexan because of the superior R factor. The insulated walls are of course vapor barriered and I covered them with tongue & grove cedar. I also made raised benches out of cedar for growing potted plants on. The floor has ceramic tile on it and the exterior is colored metal. I also ran underground power to the building and installed a fluorescent grow light. Surprisingly a small 110 volt heater keeps the temperature above freezing even during our awesome -40 winter temperatures. If the daytime temperature is anywhere near or above freezing we have to keep the screen open in the door or it overheats inside. I have attached links to a few pictures of the almost finished product, ready for another winter full of flowers and veggies. I initially used clear vapor barrier until the twin wall polycarbonate showed up. This worked rather well.
I have posted this in the comments section as well, but I think it belongs here.