How hard to reroof single garage?

[Andeh]

We ran out of monies building the house, so the single garage that existed with the original bungalow was left as is. 3.5m x 6m low 30 degree ish pitch. 

 

Recently we now want to tidy it up. I got a quote for £6500 to strip the roof back, and replace with a warm roof single sikflex membrane to match the house. Same company who did the house, and they were brilliant.

 

I like the idea of a warm roof as it visually ties in with the existing house, and gives some insulation to the garage, which will eventually become my workshop. 

 

I'm pretty handy with most DIY job, so I can't help but think I could give it a go... However the sheer price of what they're charging has me concerned I'm underestimating it. 

 

I figure it's just a matter of stripping off tiles, felt back to A frames. 

 

18mm ply the roof, 50mm PIR, ply wood again, prime and apply membrane. Soffit and fascias screwed in. 

 

A long weeks worth of work for me, but I don't want to stitch myself up! 

 

Any thoughts from the group? 

 

(ignore the odd roof coverings, it's me checking water ingress)