The best way to construct this is to use standard size rectangular frames from 25x50 mm (or heavier) section treated baton. The panels can be fixed together to form a run of what ever size you wish.
To ensure it has right angle corners it's best to have a right angle clamp and butt lap the baton. Fix the corners with triangular fillets of 3/8ths ply or thin baton nailed to the baton. While the corners are clamped position the triangular filets over the corners and fix with a 25mm bradawl firing nail gun or nail. Tack nail several times for each corner in turn and then screw through with countersunk screws (as the bradawls will rust through with time). Drill pilot holes in the filets to prevent the screw spliting the wood. Cover in 25mm X 12mm 19swg weldmesh NOT chicken wire. Use heavy duty staples in a staple gun to fix the weld mesh to the baton.
The roof can also be made from such panels though it's also useful to have a covered section and corugated bitumen roofing panels (if you can get Onduline this is excellent for this application) are light and provide shade and shelter under which the feed can be hung. You are best to slope the roof so rain is shed as the roof will sag with time. It should be supported on a frame to minimise sagging. When fixing corrugated board ensure you drill and fix through the peaks of the corrugation as rain will come through any holes in the troughs. I wouldn't use transparent board as it doesn't provide shade. A good alternative is to use mesh panels covered with a heavy polythene sheet. Damp proof membrain is excellent particularly if you can get an offcut. Vynol swimming pool liner is also good if you know of a local swimming poll installer who may have a scrap old liner. Tarpaulins are cheap too but tend to fray and need to be renewed annually. Hold down the sheeting with either bungees or a length of nylon rope with hook one end and a tent guy rope rubber tie band attached to a hook the other so some stretch enaables you to tension the rope. You can buy the rubber guy rope ties from camping shops.
When assembling the run you can use posts driven into the ground to form the framework with panels stretched between them which makes a very strong run. Make sure you include a pophole to the outside world and ideally the roof should be hinged or removable for your access.
Use treated wood and reapply preservative each year.
Happy constructing
HF