PLEASE REFER TO ATTACHED SKETCH WHICH CONTAINS SOME QUESTIONS BAGA  RAISED. 1. Normally furring channels/top hats are used to fix cieling members cladding etc. Normal depth is 40 mm. 2.Always model the gutter gutter sizes are given. 4. over all height is given as 450. You can use 450 when cladding comes it will slightly different. It does not matter.