I know that it couldnt really be that hard making a custom box for 4 12'' speakers but my question was how are you suppose to cut the hole for the speakers and about how much would you spend on wood?

Mark your middle point of the circle, and take two pencils + string (or a protractor/compass, etc), put one in the middle, and draw a circle around it.

Many subs come with a template as well. Or conversely draw a 10" 12" etc semi circle on the computer, print it off...

Then grab a saber saw, or band saw, or sawzall and cut away!

or have me build it for you, I do custom boxes..

get a piece of wood

divide the measurement the manufacture gives you by 2 so say 12 would be 6 etc etc

now measure that onto the wood

make one mark at 0" and the other a 6"

drill hole at 6 just large enough for a pencil or pen to fit thru

drill hole on other side for screw

screw wood to box

insert pen

draw a perfect circle every time..

I remember the days I had to do the wood temp. You can also use this wood temp. trick for your jig saw and circles come out great! Now I have the rotzip, alot faster and perfect!