What type?
I've just read about some builders filming there abilities on Youtube so search you might be lucky.
Just remember to check with you local authority building control office on materials they want used including insulation and the porch max height from ground to top of roof.
If you don't obtain the end pass certificate you could have problems selling the property as it is most likely to be asked for as its an addition to the standard property design.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix roofing.