Roofing Sheets instead of Slates?

[tyddyn]

Any ideas on roof covering for my cottage? Bought the place with half of the roof missing (well not really missing, the slates were all neatly piled up but the timber was absent). The other half of the roof consist of second-hand 'tin' sheets nailed to purlins (no rafters).
The missing part of the roof has been replaced with purlins, rafters and 18mm plywood, with a temporary cover of polytarp.
Being financially deficient, I can't afford to have the roof slated for a couple of years or more. A roofing sheet called 'Onduline' seems to be reasonably priced, available and easy to work with - but will the chap from Building Regs have a fit if I use the stuff on my roof? If I could use it, would underlay felt still be required?
Last point - my rafters are 150mm deep, what insulation would be suitable to fix between the rafters, comply with Building Regs. and allow me to have a ceiling at rafter level?
Ideas and constructive comments very welcome, thank you.
Graham.

 

[Deluks]

Well unless he's gonna lend you the cash, there's not a lot he can say. I wouldn't leave it a couple of years though. Tell him they are just to get you through the winter as you don't wanna be getting the roof done this time of year.

Definitely put some felt over the ply.

Having open rafters is all well and good, but you will still have to keep the joists which triangulate the roof, unless your roof is specially designed/constructed to not need them, or if the span is very small (usually under 12ft)

Regardless of rafter depth, you will still need insulation between and under them, to comply with regs. Recommended depth can vary; using kingspan/celotex, go with 4" between and 2" over, to be nice and toasty.
You might be able to go full depth, for a 'warm roof' but that depends on the detailing of the roof construction.