Leamington lofts are unusually varied, because the town has three quite different roof types and the Regency one is the awkward one.
Behind the parapets of a spa era terrace the roof is often not the simple pitch the street elevation suggests. Valleys, hidden gutters and roofs that drain inwards rather than to the eaves are all common, and a conversion has to work around drainage that is already there and already the weakest part of the building. It is entirely doable, and it is not a job to price from the pavement.
Victorian and Edwardian housing gives cut roofs with usable space, subject to head height, which needs measuring rather than assuming. A roof can look generous from the hatch and still leave you short of two metres along the walking line once the floor build up and insulation are in.
Later housing out through Lillington and Whitnash is trussed, which means the structure gets reworked rather than strengthened. That is normal work but it is not the same job as a cut roof and should not carry the same price.
The permitted development volume allowance is forty cubic metres on a terrace and fifty on a semi or detached house. A dormer facing the road is not permitted development anywhere, and in a Leamington conservation area anything altering a roofline the street can see will be examined closely. Rear dormers and rooflights are a much easier conversation. Our loft conversion page goes through the structural options.