As the housing market is in decline in the uk am thinking about extending rather than buying new.
What is the going rate for a loft conversion with single dorma plus a rear extension of say 5 square metres?
I'm not in the UK so I can't comment on local rates but it will difficult for any contractor to give such a rate. The type of construction, choice of finish materials and lots of other factors will determine the rate for your specific project. My recommendation is contact a local contractor.