Heating - what about keeping warm in winter, cool in summer.  Radiators & plumbing etc are not free! (there's a good article here: Should You Fit Underfloor Heating in a Conservatory?).

orangeries or garden rooms and different designs will use different materials will come at a very wide range of overall cost (view this cost guide UK)

Go to a comparison site like www.orangerycost.co.uk and get free quotes from certified installers. You cannot underestimate the value of getting the site inspected and having proper written quotes for the work