well ... lasani phat iss liyay jaata hay .. because carpenters available at car audio shops making enclosure with a very low quality lasani etc ..
if u buy a good quality lasani which is almost double price then the other .. and use wood screws instead of nails ... use wood glue ..
use drills for holes ...
the box u made will be expensive then the box available in market .. but it last long ..
chip board is another option .. but again u will see qualities of chipboard available .. u can use one side lamination with is more tougher then other ..
and for dimensions .. made an enclosure as per manual .. and give proper RMS to your woofer ...it will works
of u can use online calculators as mentioned by roms bhai