Garage roof replacement

[davecooper]

Many years ago, I replaced an old corrugated asbestos type roof with corrugated bitumous sheets on my common prefab type garage. Like the original roof, these were bolted to the two angle steel members that run the length of each side. This seemed like a good idea at the time, however, I have since realised that these are not designed to be used like this and over the years, they have sagged between the supports and have split so now leak like a sieve.
I need to replace these with something that is rigid enough to be fitted by bolting to the steel structure again. The choice seems to be plastic or steel. One of the other problems I had with the other roofs was water leakage through the bolt holes which I never really solved.
I want something that can be fitted fairly quickly and that can be fitted as I remove each of the old panels. The roof has a peak and a shallow pitch. Any advice on what to use and how best to fit it would be welcome.

 

[DIYedboy]

Steel sheets are likely to attract condensation, why not use the modern equivalent of asbestos sheets which are made with cement

 

[davecooper]

I am going to go with cement sheets as you recommend. I was not aware of these before but they seem ideal for what I want. My only problem now is the fixing. The original asbestos was fixed with roofing bolts which screwed into drilled and tapped sheet steel hooks which secured the sheets to the metalwork of the garage. The bitumen sheets were secured with nuts and bolts through holes drilled in the angle framework of the garage. I want to do something similar with the cement sheets but need something to fit underneath the bolts outside to seal against the roof panel. Last time, I adapted caps that were designed for screws, to take roofing bolts. However, this wasn't totally successful so any advice would be appreciated.

 

[foxhole]

http://www.screwfix.com/p/corotherm...ykVEMrxi0yUwq99rJ-ZirijdZl5uEHz5pf9Fxtk3w_wcB
http://www.plasticsheets.org.uk/fittings-and-fixings-for-3-corrugated-pvc-sheet-1638-p.asp
Though I would sheet the roof with osb deck makes fixing much easier.
If you had done this under the bitumen roof is would have given it the required support.

 

[davecooper]

Would a felted OSB roof be an option with the boards being bolted directly to the steel frame using countersunk screws. I do not really have the time to faff around with purlins and I hope to replace the garage in a few years time anyway.