The only thing they seem to leave out, is ceiling insulation, which is important innorthern climates. I don't put down insulation in the floor, but do use a rubber stall mat for comfort.
If you make the top 36" in width, you can use a single piece of "ice and water barrier" or similar to ensure it won't leak even if flat (or very low pitch). I find that 1/4"/foot is sufficient to prevent pooling of water, but still allows the dog to lay on top.
I personally don't hinge the roof, just make it lift off. I run 5/4 x 4 trim board. This allows me to prop the roof up on 2" blocks in the summer for ventilation, but still have rain protection.
If you've got a chewer, you'll need to put metal edging on outside corners--wallboard L trim works well and is inexpensive.