I gathered up all the bits of 12mm MDF I had left over from other projects and cut it into 150mm strips with a table saw. I reckon you'd have enough to make a full set of 7 blocks from an 8ft x 4ft sheet.
I marked out the lengths allowing for a bit off each end, and ticked them off my reference sheet as I worked. It's a good idea to have a few extra lengths handy as the occasional cock up is pretty inevitable.
*UPDATE* If you haven't got a table saw don't do this with a jigsaw...Use a hand saw, a square, and a tonne of patience. You really do have to be spot on, and there's too much flex in a jigsaw blade */UPDATE*
They then got cut to length on the table saw using a template piece for each length to ensure they came out the same.
Take your time with this. If your pieces aren't spot on it'll have a knock on effect on the angles later.
Then with a couple of passes through the table saw I cut rebates for the back panel into each piece. Alternatively use a router with a rebating bit.
USE THE BLADE GUARD ON YOUR TABLE SAW!!! I only took mine off briefly to cut the rebate for the back panel.