We use pallets for EVERYTHING. We build our 'mini' barn out of pallets! 16'x12' the only thing we paid for was the roof and we bought 2x4's for the roof frame. Recently we put up OSB for siding. It's divided into two stalls with pallets as the dividing wall.
Our buck's shelter is temporary - pallets on 3 sides with tarp covering it really good on the 3 sides. I use the longer pallets so it's about 5-6' long and about 4' wide.
We have a lot of wood from trees my husband cut down, and he took the wider pieces, and cut them into short pieces about a foot and a half long or so? He buried them in the ground, and set the pallets on those, sot hey pallets weren't on the ground - they will last longer doing this. Just make sure everything is as level as you can make it.
You can block the space up under it with rocks, scrap wood or just put a really good layer of bedding so no draft comes in under it. If you choose to do it this way of course
I'd either do an A framed roof, or I would just do a slanted roof. Our temporary buck shelter has the slanted roof, the east side is about 5 inches or so higher than the west side, his entrance is on the south side. Our weather this time of year comes from the west/northwest, so the shorter side gets the brunt of it, and IMO it's best to make the shorter side where the weather comes from.
When I redo his, it will be about the same size, just permanent, and he'll have a doorway - the front won't be completely open like it is now.
Cover it with OSB, and there ya go! If you get it done, go to Lowes with your measurements and they can cut it for you. Just be sure to take a permanent marker with you to makr the pieces so you know where each piece belongs!
This is what I plan to do when the time comes to get his house done
As for covering the top, I am not sure if you want to use tile or what? I have no real experience doing roofing, and don't even know what I'll use. You can look on craigslist or place an ad looking for roofing materials. Until you find something you can also cover it with tarp. I love pallets, osb and tarp LOL
Our mini barn:
Here's some pics of when we started. I don't have any current pics up yet...
You can get an idea of what I was talking about whenI said don't set them directly on the ground <So they don't rot and become weak>
http://www.flickr.com/photos/24553848@N ... 846021045/
You don't have to put them so high above the ground, this was just my husband's preference, because he surrounded the area with rocks, and dirt to build it up. Our goats LOVE walking on the rocks...