I built this little contraption onto my trusty (made in Japan) Vivitar 285HV.
I just measured it out on matte board, cut it to size, and taped it all together.
Materials used:
-wax paper 4x5 neg sleeve(s) x 2
-matte board (black on one side, white on the other)
-gaffer's tape
-matte knife
It's not the most sturdy thing, and i'm sure it wouldn't handle a drop too well (nor a strong poke), but it works pretty decently. Now I need to modify it to be removable and possibly collapsible for portability.
Examples shot:
Canon Rebel XT (350D)
Vivitar 285HV flash
with DIY mini-softbox
and off-shoe cord