building a box

A couple inches will not make that big of a difference. 

so what you think is the best thing to do

Best as in best sound, or as in more practical false door and space wise?

both. i def want the best sound and will work around that with the floor f u think making it to shollow will hinder sound

or should i just keep the box i have ad work around it.i really want to save some space but if that is going to affect the sound u think ishould build it?thanks

That is really up to you. Do you want the extra space bad enough to build a new box? If you do build the new box, is it more important to have the best sound possible, or is the maximum amount of room more important? If you can't decide, maybe you can build 3 different boxes and try each one for a week or so, and then decide on one. I can only tell you what works and what won't work, but you really need to absorb all the info and make your own decision.