Please help: DIY roofing!

Hi, I'm basically turning a single storey flat roof, that runs along the side of my house, into a pitched roof, but also extending to cover an area once occupied by an oil tank.
Roof will be clay tiles to match existing roofs.
I'm unsure about;
1) Attaching rafters to the side of the house. Is this just screwing a ridge board (6" x 1") to the side of the house and nailing the rafters to it, tiling, then covering with lead flashing?
2) Attaching the rafters to the double brick solid wall. Another single storey part of the house has a 3" x 4" wall plate, offset slightly from the innner course of bricks, then a row of bricks on the outside which, because the wall plate is offset, overhang the edge of the wall by 1-2". Should I just copy this?
3) One end of the new pitched roof will butt up to a flat roof (not replacing it all). I was thinking of exterior grade ply attched to rafter and vertical down to flat roof, sarking, laths, pvc cladding, with flat roof covering tucked under the cladding.
4) If I use a purlin do I need ceiling joist (to stop the roof spreading). Span is 2.2 m and pitch 43 degrees, ish.
Thank you, Neil
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