If you have time and energy, and ideally a vehicle, it should not be too difficult. The key is to SCROUNGE STUFF.
Plywood and 2x lumber pieces are not difficult to come by (ask at construction sites, they sometimes discard old concrete form materials and leftover bits of roof decking and such; and keep an eye on the roadside as you drive around in daily life; and check out garage sales and tool/junk or contents auctions). You can also often get free, or at least cheap, windows and used roof tin and leftover shingles and paint and hardware. Screws or nails you will probably have to buy.
The hardest thing to scrounge in most areas is run fencing... if you have farm-contents type auctions in your area, that's the best place to look, or occasionally you'll see people selling used chainlink for cheap [check to make sure it's in usable shape tho]; but you may end up having to pay full retail for fencing.
Pallets can also be really, really useful and often free. (But ask first!). Some people have built fairly large coops almost entirely out of free pallets. If you want to explore this option, DO NOT google around and set your heart on a particular design that someone else built. What you need to do instead is start collecting pallets, preferably plain unpainted untreated-looking ones that are built with a substantial amount of wood. Then once you got a bunch, see what their properties are. If you can disassemble them without ruining most of the wood, that is an option; but in many cases you can't, in which case think about designs where you use them in a modular sort of way. How many of them are the same size/shape/structure as each other? If you have a bunch all the same, you have more freedom of design; if many of yours are different dimensions or structure than the others, you will have to exercise more creativity and may be limited in what designs you can build. There are a bunch of threads on pallet coops so I will not say more here other than: don't forget structural soundness. Just cuz you can stack it up and it can be screwed together and sorta stay that way for now, does not mean it is really sound enough for an animal-occupied long-term structure.
Good luck, have fun,
Pat