Final invoice for shell construction (200 sqm, clinker, without basement, roof) ok?

The contractor must document the hours of his employees. Have him show you the schedule of when who was at the construction site and check based on your memories from site visits whether this is realistic. Maybe you can particularly remember certain days well and check their timesheets. I would definitely do this, and if in the end it's only 10 hours that you can deduct, you have still saved 400€.