this is just a thought cause I'm "cheap" to begin with. If you have the time and want to make the extra effort. Scrap lumber is fine. it's a chicken coop for cripes sake. I used old pallet wood for most of the insides. Takes time to break them down. but you'll have the uprights. 4 sheets for 1/2" X 4 X 8' plywood for some sides and cubby's. Then add in 4 ea 4X4X10's for the corners. To save money and budget start out small and add to it over time, make your design such that you won't have a problem adding on later . Get em in a place where they'll lay. I have two sides of the coop with wire mesh starting half way up. That way it vents' in the summer and then I drop the inside "ceiling and add -plastic sheeting in winter so it's easier to keep warm. Well 20 + is warm in Montana in the winter. I'm thinking $500 is about right. I also placed a rubber mat, the kind you find at a Murdocks type store for horse trailers, on the floor. It makes it easier to clean. Oh, I also found old carpet to line the lower walls with so in winter it helps to keep the heat in. I asked and not a one of them has complained. Although when the chicks hatched and saw what they had to call home, they did call me "cheep".