mandyp if it helps, weve just had the quotes in for having ours done, as follows:-
1: general builder, who it was beyond and out of his nornmal scope..20K just for labour!
2:- specialist loft company, took one look at thedrawings 27k, and only because he had a spare slot, otherwise 30k. when i said i would take care of plumbing, electrics, plasterboarding plastering and insulation he was prepared to knock 3k off!
3:- roofer who now does loft conversions, took drawings away and prced it all up - 18K up to a first fix so i can do the rest as above
guess which one i went for! sort of proves my point about specialist companies!