Bartlomiej chmielewski
To do a dormer you will require architect, carpenter and roofer. Architect will design the structure to comply with the current building regulations. All other trades will work in accordance with those drawings. Roofer (to prevent any unnecessary damages) will remove roof covering (roof tiles or similar) and will cover the roof after dormer has been build. Carpenter will cut into existing structure with new impregnated C24 timbers. You will also need to arrange windows to be fitted which must comply with building regulations i.e. have a trickle vent, opening above certain height. You should also get an advice from roofer if scaffolding will be necessary. Regarding your planning permission. It varies on a type of the building. Please check planningportal.gov.uk/permission it should give you all necessary answers and if you are still confused give a call to your local planning office. On a interior side you would have to get a plasterer and painter to complete the work to your satisfaction. Hope it helps.
