This - How To- video from Patty is a good one for those who are interested in building their own raised beds but don't know where to start. The best wood for a raised bed is cedar which is quite rot resistant. Recycled boards can also be used. Craig and I used the old boards from Geneva Greenhouse that were used when the snapdragons were grown directly into the ground. They were "cured" nicely and haven't yet shown any sign of rot. Our beds are about 4ft wide by 12ft long. We didn't add any wire to the bottom and haven't had any trouble with animals burrowing underneath. We also pounded the corner "support" wood into the ground to keep the beds from moving.
We allowed 3ft - 4ft isles between our beds to allow plenty of room to harvest or crops, push a wheel barrel through or just relax in a chair on a warm summer day :-)
A raised bed can be placed anywhere one pleases as long as it gets at least a 1/2 a day of sun for plants that require sun. So, pick any spot, even in the middle of your lawn! Just line the bottom of the bed with cardboard or several layers of newspaper. The lawn will not live under the layered paper, compost and soil.