Kfen-
All of my turtles and tortoises are housed outside (tropicals come in during the winter, others remain in their pens and burrow under). Here are a few pics of some of my enclosures I had on my computer at work. I'd be glad to try and dig up some others or provide more info if you need.
Each of my pens is constructed of pressure treated decking board (1x6). I stack them usually 3 boards high, braced with 2x4s or 2x3s. I put a brace at each corner and about halfway down a long run of wood to keep it from bowing as it cures. They may or may not have a lip on the top (depends on the species).
Here is a pic of the very first enclosure I built. Why it is on my computer at work, I have no idea. But you can see the general construction of the wood. I put the long sides together first, set them in place and then added the ends, securing it all together.
first pen by
B Boone, on Flickr
I use essentially a riff on the same idea for each pen, just changing the size of the layout. The smallest pens are 4x4, and go all the way up to dividing the main yard.
A series of box turtle pens:
boxes by
B Boone, on Flickr
Juvenile stars:
juvie stars by
B Boone, on Flickr
Pancakes: (note the lip at the top to keep climbers from getting out)
pancakes by
B Boone, on Flickr
I've recently changed my style of fencing for my Manouria, after seeing some fencing in Myanmar that I thought looked really cool. I'll have to take some pics of it this weekend and share. It is vertically oriented, different heights and widths of wood (1x4 all the way to 1x12 wide, and varying from 16-24" high). I think it is kind of cool looking.
Anyhow, hope that helps. Like I said, I'd be glad to show some more pics or answer any questions you may have arise.
--Berkeley