Changing from traditional roof to SIP

[Linto]

I need people's thoughts on the possibility of changing my roof design for our loft extension from a traditional rafter roof design to a SIPs one.

My thinking behind this is that we've been quoted >£25k for a temporary scaffolding roof and this is just destroying our budget.

I'm thinking of speeding the build up and one way if doing this could be using SIPs instead of the traditional rafter design we are currently planning for. 

I know they will be more expensive initially but if i can save on the cost of the temporary roof due to the increased speed to water tight and just accept that we will need to repair some rain damage plus the cost saving in labour it should work out cheaper?

Plus from speaking to a number of builders materials that are imported seem to be fluctuating in price and availability which is complicating their ability to quote properly, SIPs being built here shouldn't suffer from this?

What do people think, how easy is it to change construction methods from that in the original plans and would it be worth it?

Edited February 1, 2021 by Linto
Added more details

[Conor]

Check out thermohouse roof panels, we had our house designed for them and then changed to a cut roof at the last minute as our builder wasn't familiar with them.... no structural changes needed. I think they can support unpropped span of 4.5m for a typical roof.