3/4 high density particle board is a popular material as it is dense and strong when used in small (less than 3') boxes. I have used double thickness board also but that may have been overkill. I usually try to find cull lumber at the local big box home improvement center. Cheap!!! They can cut it for you but be prepared to fix the tearout. Bondo works well. I use a fine toothed circ saw for my straight cuts and a jig saw for the speaker cutouts and the connections. Good glue is a must (Elmers wood glue or better). Gorilla glue is fantastic as it is super strong and seals gaps but it aint cheap!. If your cuts arent perfect I would recommend using caulk on the gaps and on every inside joint you can reach. If you want to recess the speakers but don,t have a router try using thin plywood for the top (1/4) glued to 3/4 particle board underneath. Cut the plywood speaker hole large enough so the speaker will mount on the particle board underneath. Fasten every thing with screws and pre-drill all holes as the stuff splits easily and so your screws dont protrude. A predrill bit can be bought where you get your wood just make sure it matches your screws. Solder all connections inside the box. Sand any rough or sharp edges before covering with carpet. When measuring dont forget to add or subtract for the thickness of your wood. I get the other parts at the local car stereo shop and use the best I can afford but you can always upgrade the speakers later. You can get parts from blown speakers and use the wood form them as templates for the cutouts. So basically you are building a box with holes in it! Don,t expect your first box will be perfect. Make a few small boxes to practice (simple tool box, parts box, dvd holder...) The bet way to learn to do it right is to screw it up a couple times first. Also try the local library or Radio Shack for books on the subject. Then make an instuctable!