I just recently took up coop building as a hobby and spend a lot of time configuring how to cut down on actual cost while maintaining a strong, reliable structure. I've started doing some with 2 X 3's ($2.04) instead of the traditional 2 X 4's ($3.26) So the saving is substantial for framing. Corrugated PVC roofing panels ($14.50) I only insulate the floor and roofs in mine, a lot of the rigid foam insulation I used is just going around to factories who throw that stuff out as its just packing material for them. Windows if you add some can be found at yard sales and just plain free from the local area. Clean them up, re silicone if necessary. My latest I used 1" tongue and groove boarding for the exterior which I kept visiting my local home cut lumber yards. One had a pile of 500 sq. feet that had been left outside for most of the year. $80 with free delivery. Had enough to do four walls, two doors and the roof. I saved several hundreds of dollars on that alone. For siding cedar shake is a good bet if you go that road, chicken coops don't need the high end heart wood type which is very expensive. I use the mid grade version with I get locally for around $18-20 based on supply. Another great example is my good buddy cleaned out a retired carpenters garage and he got to keep mostly everything he took out as part of the deal. I managed to get 2 4 X 4 pressure treated post for free which I use for the legs on my coops. So many great options around you just have to do the leg work to find them. And you can still make a great product to be proud of with just a little more effort.
here are a few more pics
