You will be able to fit the A1200 motherboard and extras inside the "SilverStone Milo ML03B" and fit extras without problems
Case dimensions:
440x340x105 mm (W/D/H)


That case is quite cheep also
if I would do a A1200 desktop case ill use something like that 
Cutout a new back for I/O's, new mounting holes and the motherboard is set, if you want a CD/DVD-drive it has a spot for it, you have to mod to get a internal floppy but not to much work, I would probably put the floppy in the 3,5" HDD cage under the 5,25" facing left or make a cut out in the right part of the front for a floppy.
I quite like that.
Thanks, I was looking for something to mount a small custom board into.
Anyone else got any suggestions?
The board I'm considering could probably be scaled back to micro-itx or up to MATX.