Just toying with an idea. If you could give someone details of your house and a basic floor plan (or link to rightmove) and they drew up a new layout based on your needs (open plan/extension etc), within permitted development and give you some 3D images based on actual location, how the sun moves throughout the year etc. and a rough idea of costs?
It would still need structural calcs etc and proper drawings if you actually went ahead but it's more a quick and cheap way to see the potential that a house might have without paying the full price of a detailed design by an architect or builder.