Let me tell you a story. Many years back, I noticed one of my sons did not know how to swing a hammer properly. Since I needed to replace my lawn mower storage shed, I got one of those kits, 8' x 10' if I remember correctly. My sons, ages 10 and 12, put it together for me. They read the instructions and did all the assembly, including the shingle roof. Everything was precut and the hardware was all included.
When it was finished, one corner did not fit perfectly, but so what, it didn't leak. And later on they impressed the other Boy Scouts when they were helping on the Eagle projects because they knew how to swing a hammer with one hand and hit the nail instead of their hand.
If they can do it, you can do it.
I'll admit the ventilation and the window can be a bit harder. What I'd do for ventilation is cut the boards that go on the sides maybe 8" short under the overhangs and cover that opening with hardware cloth to keep things from climbing in.
For a window, you can maybe get one off Craigslist or something like that, but an easy way to make a window is cut a hole out of the siding between two studs. Put a horizontal piece of wood across the top and bottom of that opening between the studs so you have a flush surface, then cover that with hardware cloth. You could get a piece of plexiglass to cover that opening in the winter if that were a problem for you.
In Alabama, you could proably leave off a whole sheet of the wall panel and just cover that with wire. That would need to be on the downwind side, probably east, and put the roost near the opposite wall where they don't get rained on and are pretty much out of any breezes. In Alabama, your danger is not going to be from the cold in winter. It will be from the heat in summer, even if you live in the north, like the Huntsville area. You need lots of ventilation.
I know it can feel overwhelming, but you may surprise yourself at what you can accomplish just by trying.