Bigger, and deeper, is better for acoustic builds, for a better sound. But for electric only, not so much.
No such thing as "too big" :-) Seriously, x2 Keith Rearick. That'll shine as an acoustic - especially if you brace it!
Just a bit more detail on the last reply: more surface area means more resonating top surface means a broader tonal spectrum. A thru-neck design mitigates this somewhat, but all things being equal, it still holds true. Depth gives you the air pump activation, so the deeper the box, the more air you get bouncing back from that top against the back. From my experience, 2 inches is a minimal depth for an optimal acoustic instrument. Like Keith said, deeper is better if you're reaching for the uke / parlor guitar leagues. When I say acoustic, I always assume throwing a piezo under the hood, but if you're really jonesin' for electric, that depth would make a great electric-acoustic rig with one neck pick-up allowing the back end where all the meat is to resonate, or go with a thin pup and mount it to the fingerboard floating ABOVE the top for the best of both worlds. Keep us posted!
Hi Fantacone, I don't think that the box of that size is too big, I have built using box's 14"x10"X 2". All my other boxes are 2" deep inside. I should mention that those bigger box's are six stringers. I have found that for some instruments like say mandolin, soprano ukes and violins for instance, the size of the body gives the instrument its recognisable sound.
Going bigger also relies on other features that have to be taken into consideration as well as just going deeper and wider etc.
What sound do I want? Deep/bass or treble.
More depth in the body will have a guitar favouring bass tones with less overtones [complex tone], it also limits clarity and projection.
When using a larger box with more air in the body that carries the sound waves, I find I need a top that is sensitive to the strings movement and can vibrate effectively to move all that air. Also with a larger box you have more freedom in choosing scale length's.
Here is a deep bodied guitar....
Compared to a parlor sized guitar I'm building....
Both will work but will sound different.