anybody have woffer box specs/deminsions

want to build a under the back seat box with my son but cant find "prints" or deminsions.......dont want to just "BUY" one. To pricy n Rather teach my son a little..........ive got my materials using burch n got started but i think im fixxin to ruin a good peice of wood!!!!  LOL  Can anybody help?  willing to purchase ........Thanks......oh its an 04 AVALANCH ........

http://chevyavalanchefanclub.com/cafcna/index.php/topic,115804.0.html

there ya go.