This one is easy! We had an old trampoline frame in the back yard. We just reconfigured the pieces into the frame and added a few cheap items to make the coolest chicken coop ever. Our 10 chickens and 13 ducks have lots of room, especially with the attached chicken yard.
Before: (ok this was the new trampoline :-) ) After: (what we did with the old one)
Ultimately you are just using two halves of the circle (that used to stretch the trampoline) as parallel arches, and connecting them with horizontal supports that used to be the safety-net poles. There's not a lot of precise measurement, either. mostly just eye-balling lengths and cutting them on the fly, old-school treehouse- style.
1) Disassemble the trampoline frame. It's modular, so it just pulls apart.
2) Make two 2-section arches: two pieces of the round frame on each side , pointing the leg-stubs at each other.
3) insert 3 8-foot lengths of safety-net pole into the leg-stubs on each side to connect the two halves of the outside frame. You should end up with two rectangles. The arch frame won't be symmetrical, because of the way they were built to connect the trampoline frame to its supports, but that won't be a problem. It's more important to make sure you have right angles.
4) use tie-down straps to hold the frame together at first. This will save A TON of time and will make sure that the structure remains squared-off as you are putting the roof on. I used one strap on each side to hold the 2-section arches in place, and two straps to hold the two halves together with connecting net-poles between them. make sure you have it squared off by adjusting the tension of the straps
5) Attach your first 4X8 section of corrugated aluminum. Its the sheet metal that ultimately makes the whole thing structurally sound. You want to make sure that it is centered on the first of the two rectangles. This allows plenty of overlap between the sheets, right over the horizontal supports. Use sheet metal screws to attach the sheet to the frame, starting with the outside arches, then across the horizontal support that will be closest to the ground. Don't screw it to the next horizontal support yet. A couple of tips on screwing the whole thing together- a) Use a drill and make pilot holes. b) try to get a few screws through the places where the frame sections connect.
6) Attach the second sheet in the same way- to the outside arches first (make sure that you are keeping them parallel), and then to the bottom-most horizontal support. Screw through the two sheets of aluminum into the horizontal support. Don't attach the top one until you add the next sheet of aluminum.
7) remove the tie-down straps from your first section. It should be solid on its own now.
8) add one more arch section on each side, and one more horizontal support. Hold them in place by attaching the tie-down straps to the middle of the completed section, just like you did before.
9) add the next sheet of aluminum, and so on.... repeating steps 6,7,8 until you have completed the roof & frame.
10) Build the bottom frame box. I'd recommend 2X8. You'll need two 8' and two 12' boards. The tie-down straps come in handy here again, too: put one on each side to pull the completed arched roof nice and tight, and make sure it's square. Measure and cut the frame such that the longer boards line up directly with the arches, and the shorter lengths connect them on the inside. Put it together with decking screws.
11) Create a level foundation for the box frame. I used river-rock and leveling sand, topped with some leftover bricks. You can see in this picture that I also lined the inside of the frame with bricks, to keep critters out... just in case.
11) Attach the arched roof to the box frame. I just used some old shelf brackets. You will notice that the sides are not symmetrical. There will be two stubs opposite corners that are longer than the other two corners. Don't worry about that. Just keep the horizontal supports parallel to the box frame.
12) Add the door frame on the front side. Position your screen-door in the middle, and mark where you want it to be. On the outside of the frame, attach a vertical 2X4 on each side, such that the closed screen door will have about 1/4 inch of clearance. The easiest way I found to do this is with 2 1/2 to 3-inch 1/4" concrete screws, screwing them through the metal frame, into the 2X4's.
13) Add the first horizontal supports- a 2X4 or 2X6- it's easiest if you base their height on the width of the hardware cloth. These horizontal boards need to be in-line with the box-frame and arches. I used brackets to connect the ends of these boards to the metal frame.
14) Attach the hardware cloth. Some easy tips. a) as you unroll it, just place it up against the front of the coop such that it wants to coil *against* the coop. This will hold it in place for you, and will also make sure that it "wants" to stay up against the frame. b) just mark it with a sharpie while a helper is holding it in place. c) cut it with garden shears. wire cutters take way too long! d) To attach to the metal frame, I used drywall screws and washers, screwing straight into the slots where the springs used to attach.
15) attach the other two vertical 2X4s to the outside of the coop to hold it all in place.
16) put the door on. I could give specific directions here, but it's just a door. attach it.
17) On the back side, it's easier because you don't have to deal with the gap for the door. Just use one long horizontal 2X4, in-line with the frame, at the level of the hardware cloth. Attach the hardware cloth. Screw in 3 vertical supporting 2X4s on the outside of the frame. Done.
From here out, you get the idea... I've shared all the tips and tricks that I figured out on my own. Wash rinse repeat until you have your own ultra-modern green-minded recycled trampoline chicken coop.
Oh- and hang on to the trampoline parts that used to be the legs. They make an awesome fence for your chicken yard. I'll share that part next time....
Also- there are a couple of options for where to put the actual coop inside of the structure. I built a free-standing one, shown here, from 3 sheets of plywood and some left-over 2X4