Our hen house is just an unfinished utility shed that came with our property. The chicken run is made out of recycled pallets, 2x4 posts, and wood poles we scavenged off our own property as well as a couple rolls of chicken wire. We also used some spare ply wood lying around.
There's our wee little chicken run. You can probably get on Craigslist or your local Freecycle network (through Yahoo or Facebook, whichever they're using) and find some cheap or free scrap lumber to build a hen house. You can use boxes or old wooden crates for nesting boxes. We put up roosts in the shed, they're just more long poles we found laying around, nailed them up and they work fine. We have 17 chickens counting the rooster and the hen house is way way way more than they need, it's like the Taj Mahal of chicken coops in there, it's huge, it's the size of a small bedroom.
You only need a space covered on 3 sides, 4 if it's still well ventilated, and you only need enough roost space for them all to find a spot. For 15 chickens you probably only need 3 nest boxes, 4 tops. All 16 of hour hens only use 2, though to be fair most of them are old and don't lay much if at all.
The only thing we paid for when we built our coop was the chicken wire and staples for the staple gun. The rest was just lying around, and if you know anybody who works at any kind of manufacturing plant they probably have tons of spare pallets laying around that you can take. You can pry the boards apart and use them to build something from scratch or you can nail pallets together and shove wooden poles between them and into the ground to keep them steady, that's what we did. Looks like crap but it held up to the neighbor's great dane and a few coyotes.