Would this case be for gigging? rehearsing? recording? or just practicing?
Cases are diffrent inside for different guitars, are you going to make a Strat case? a Les paul Case? or a case with adaptable parts to reshape to fit different models?
As a guitarist you will know for gigging you need a loud amp with lots of headroom, the louder the amp the heavier it gets, so im guessing you are not thinking of a gigging amp.
You could of course mike it up and go through the PA, in which case it could be very light and maybe a low output amp.
You would have the same problem with rehearsing.

The amp has to look good too, if i was designing it i would make a rectangle case in the shape of a Head and Cab, a light weight clip off front to reveal the amp under it.
Single speaker, with the Volume/tone on/off controls on the head section.