Now the walls
Frame the walls with non treated 2x4s split in half 1 3/4" x 1 1/2" to the demensions of 6' l x 5' w and 3' h, with 2 large windows on the south side and 2 full length and width doors in the rear. Spacing on the side is divided into 4 equal spaces, as one of them will be your access doors to the run.