Nearly there

So as mentioned the box has been built.
Back + 2 Sides: 700x500x12
Top and Bottom: 524x512
Door: 700x524

All I did was measure accurately along the sides of the box and screwed it together. The door was quite heavy so I bought a brass hinge and attached it that way

BASIC BOX DONE:Box without door, Box with hinged door (and knob)