Chendy

Hello, What parts of a farmhouse house renovation project legally possible to do DIY? Or with English based non France registered builders? Can you replace roof tiles DIY? Can you replace roof timbers DIY? Fitting Windows DIY? I read you have to get 'experts' for serious structural work. But wondering where the boundaries lie. Can you officially do the work, and get a builder to sign off? Any good resources to to learn about this? Thanks