Solihull has some of the better lofts on our patch, because a great deal of the interwar and older housing was built with generous roofs on generous houses.
On that stock a conversion is frequently the best value space available, since the roof and the walls already exist. Head height still needs measuring rather than assuming, because floor build up and insulation take more out of a roof than people expect, but the odds here are better than average.
The post-war housing is trussed, which means the structure has to be reworked rather than simply strengthened. That is routine work and it is not the same job or the same price as opening up a cut roof, and anybody quoting the two identically has not been up there.
The planning position is what varies most. In the affected part of Olton the Article 4 direction means permission is required for most householder development, so a dormer that would be permitted development elsewhere is an application there. In the other conservation areas the ordinary reduced limits apply, and a dormer on the roof slope facing the road is not permitted development anywhere in any case.
The permitted development volume allowance is forty cubic metres on a terrace and fifty on a semi or detached house. Escape, fire separation and stair position are all Building Regulations matters. Our loft conversion page goes through the structural options.