900x900 Diagnal Corner Unit - Laminate Worktop

Hey lads,

I'm not a fitter, just a soon to be customer, i'm sat here scratching my head wondering how on earth a laminate worktop is properly fitted above this base unit, so that i can order the correct amount of worktop. I'm visualising a small triangular joint at the back? Not a clue.

The corner unit has a neighbouring 300mm and a 600mm unit.

Also I was going to order ABS worktops, is this ok?

Thanks in advance.