I've been thinking about the design of this cabin and going back, if I could change a few things, here they are. First of all, I'd design it with the expectation of adding a bedroom sometime later in the future. That way I can avoid re-routing wires or windows or siding.
Also, when I built mine, I did 8 ft walls with triangle trusses. I messed up because I was following free shed plans I found online. Of course now, I'd do it differently if i could do it again, I'd buy one of Johns plans which had 10 ft walls with a ridge beam/rafters and balloon framing platform at around the 6-7' range. That way I'd have two floors with plenty of head room on each. But a greenhorn like I was back then was intimidated by doing ridge beams and rafters and I also didn't fully think balloon framing would be strong enough, I was wrong.
Also, I'd extend the roof over a 8x12 deck portion and make a (screened ) porch. So actually it would be a 24x12 first deck. I'd stick with 2x4 framing on a small house like this. Its incredibly easy to heat and 2x6 walls eat quite a bit more room I feel than in a larger house.
Lastly, I would put insulation in the floor, prior to laying the 3/4" advantech ply. Its a huge pain to put it in on your back in the mud, trust me.
On a side note:
John Raabe has incorporated expandability in his houses, which I love. If you're trying to save a few bucks on plans, it can come back to bite you because of all the time and effort to redo things you didn't think of. You're better off going with a proven plan that is expandable and makes the best use of the square footage you're creating. If I were going to build a house in the future again, I'd either go with one of johns plans or have my gf's father (a 25 yr architect) custom design one for her and I. But 2 yrs ago, you couldnt tell me that, call it whatever you like, I've learned now.