I'm currently making a cigar-box guitar, but in the absence of a cigar box I'm making that too. Dead simple: 5mm ply, two short sides, two long sides, a top + bottom and a few blocks to reinforce the corners.
So: I cut the sides and put a notch in one of the short ones to take the neck. Having done this, I realise that in the best tradition of "measure once, cut twice" I've been & gone & put it off-centre. Drat. But there's a handy piece of ply lying on the bench so I take that, cut it to length, mark it up properly this time, double-check it, and cut out the notch. Fine.
Then I take the blocked-out neck and try it in the notch - yo, dead centre - then do a dry-run assembly with the sides: two short ones, two long... er...
That's funny, one of the long sides has disappeared. It was on the bench just a minute ago...
I really do need to retire.
Oh, wait...