The bottom set is a lot more planned and even than the top one. The top set was a combo of 2x4's 2x2s 2x3s and random plates and other bits I could scrape together. The bottom shelf I measured and purchased the specific amount of bricks I needed. The overall length is 92 studs. The plates that form each shelf ledge are 6x4s layed end on, so 23 per level (23 x 4 = 92 studs). 4 levels so 92 plates in total. The bricks are all 2x4s. They lay across the plate level so that 1 stud is sticking out behind them and they take up 2, then 3 studs in front for the minifigs to sit on. They are stacked 5 high on each level. So 23 x 5 = 115. Three levels use them so 3 x 115 = 345. Plus a used a few extra ones as on each level a few on each end are turned sideways to achieve the offset to make them overlap like a brick wall. The top level is actually 1x2x5 bricks. I used them as it was lighter, slightly cheaper, and on the top I didn't need 2 studs depth to accomodate another step on top. The top of them is crowned with a layer of 1x8 tiles to keep the tall bricks in alignment. Could use thin 1x? plates but I needed tiles as the studs from a plate made it just too tall to fit into the shelving unit. There is also a bunch of bricks at the back on each end coming down from the top layer to the floor and attaching to each level. This is needed for stability otherwise the whole thing topples backwards. It's not pretty but it does the job, and you can use any random old bricks you have. Hope that helps, let me know if it's not clear or you want more info/pics.