We used cement rebar to make a frame for the roof. We used zip ties to attach the edges of the rebar along the sides of the kennel.
Then PVC pipe was bent along the roof, again using zip ties to attach it to the rebar, and to the sides of the kennel, for extra strength during winter when we got a lot of snow.
1X2 boards were attached along the sides with zip ties, so that the plastic could be stapled to them.
We attached 1X2 board around the door of the kennel, so that the plastic could be cut along the opening, making it so that the door could be opened.
It was then wrapped in 6 mil plastic. The plastic was extra long around the bottom, and we put dirt on top to hold it in place. When it would get too hot inside, I could easily lift the dirt off to give it some good ventilation.