I just got a 15 inch 150 watt eminence commonwealth speaker (bare speaker), and I'm planning on building, or converting an old cab for it. I was wondering a couple things: mainly what types of wood are usually used for guitar speaker cabs and where can I find the correct wiring (including clips for the speaker prong thing and the quarter inch female jack), I've looked all over except for online. Any suggestions or recommendations would be greatly appreciated.
The cabs are usually made from some 12 to 20mm plywood - depending on the size and weight. Plywood combines some resonance capacity of wood, but retains extreme mechanical strength - I think that is why everyone try to use it.
So you'll need a plywood box or a sheet of plywood. If you can't lay your hands on a 18mm one (pretty common for guitar cabs), you can get some thinner sheets and then glue them together.
Basically you'll want to search the web for some cab blueprints to have some basic ideas on how to build one (pretty lengthy to explain it in text).

The wiring for a single speaker is extremely simple - the female jack has two taps, the speaker has two taps... well, you get where I'm going

Personally I buy thing online since there are many different types of items I need to build my amps so its just more convinient when the stuff arrives and the local post office.

parts express sells almost everything you will need. i build out of pine oak and maple for my cabs. a 1X12 i believe my dimensions were 18"H x 21-1/2"W x 11"D and you can just scale that up for the 1X15