Converting flat roof to pitched

Hi, my garden brick shed has got a flat roof which is well by its sell by date and leaking.....I am not a great lover of flat roofs and would like this to be pitched so I am going to build up the gable ends and put a framework for a pitched roof. Although I have basic diy skills I am a bit unsure how to lay the frame work out and then the batterns and then the tile positioning, does anybody where I can get some sort of roofing for dummies info or possibly a idiots guide........and any advice would be welcome. Thanks, John

.......wall plate, straps, rafter, ridge board, joists.

what more do you need to know?

Thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!