Who coordinates for you that the roof is installed on time and the insulation between the rafters or similar is done promptly/simultaneously? What do you understand by the 240 sqm? Living space or ground area times three? If the cistern is included: are all other ground works (excavation; laying of the underground pipes, to which the rainwater pipes then connect, etc.) included? Who coordinates that for you?
For comparison: we received offers of about 200,000 (+/- about 5,000) each for a ground area of approx. 9.6x12 m, basement/ ground floor/ upper floor/ attic for all earthworks, shell construction with chimney and concrete stairs including roof structure, including prefabricated garage and carport. (whether you can really compare that now, I leave up to you ). The offers did NOT include structural engineering and architectural services, but due to the "extended shell construction" we had the advantage that the main provider (shell constructor) coordinated the earthworker and carpenter for us. Separate awarding of these three trades would probably have been a bit cheaper, but also significantly more potential for errors in the process and considerably more time expenditure for us.
My conclusion: -> get one or two more offers with the same scope of services -> such an extended shell construction including roof also has advantages