Each block is 6 x 10 lego units, I already had the 6x10x1 grey bases (two of these per block) in my loft. The white blocks I bought from
this ebay listing (6 of these per level), but the blocks around the back that you can't see are older ones from my loft stash. The Flat tiles on the top of each block are from
this ebay listing, 15 of these per block (the block at the back has flat tiles I already had).
Regarding the grey colour, I've done some quick googling before just announcing they are just grey
The 6x10x1 panels are original Lego grey, but apparently Lego changed their grey colours to a more bluish grey in 2004, and Lego aficionados called this bley lol The blank tiles (part number 3068) I have are Medium Stone Grey (Lego colour ID 194), aka light bluish grey / light bley.
The 6x10x1 plate part number is 3033, and the iconic 2x4 brick is 3001.
My 24" Dell monitor is therefore sitting on 6 3033's, 45 3068's, and 90 3001's
More info than you probably wanted lol