Roof terraces

Currently interested in a house in Portabello; the one obvious downside is the very small and overshadowed outside space. It has a small new-ish single-story flatroofed extension. A few of the neighbours seem to have roof terraces on their extensions, which seems like potentially a nice solution to get a bit of extra sunnier outside space. Does anyone have any idea how expensive it’d be to put in such a thing? I assume it’d require reinforcement of the roof.

You wanted to. Don’t deny it. No judgement here