I see that the 1.5 story plan can be modified in 2' increments. Is this also possible for the single story plan? I am considering purchasing the plan, but would like to build 20x36 instead of 20x30. Is this easy enough?
Building longer is much easier than going wider. Basically you just add more foundation, walls and roof, repeating sections of what was used in the original plan.
I built the single story, you will have no problem extending it longways.
I used 16" floor joist increments since the 2x12 SS was the sturdiest dimensional lumber I could get ahold of at 20' span, might be able to use 2' increments with engineered lumber.
If you're not married to 20' width and you're just a single guy, I did find obtaining and hauling 16' lumber to be way more accessible from both a logistics and accessibility standpoint, but given this house was used for more than one person the 20' suited us perfectly.
Thank you both very much for the replies. I do electrical work by trade, but I have very little building experience. I'm going to contract some of the work, but I'll do as much as I can. These are some good points I hadn't considered before.