ᐅ Flat Roof Renovation on an 80 sqm Older Building

Hello,
We would like to have the flat roof of our older building (built in 1970) completely replaced. We are currently gathering quotes. What approximate price per square meter should we expect for the full removal and reconstruction of an 80m² (860 sq ft) flat roof, including KfW funding?
Best regards,
Basti

What do you mean by complete? Including the ceiling structure inside and outside, or just sealing and insulation?

If the description for the companies is as clear and detailed as your question here, then the quotes are worth just as much as the answers here.

400 euros per m2 (10.76 ft2)

A proper estimate can only be made if a roofer inspects the roof structure on-site by opening the roof. Anything else is unreliable—how can you provide an accurate quote if you cannot assess the scope of work and, importantly, the STRUCTURE of the roof and what exactly needs to be done? Demolition, wood, insulation, fascia, guttering, etc.

It already starts with the height of the connections at the patio door and wall junctions; a 15cm (6 inches) clearance must be maintained above the waterproofing layer.

So I now have two offers, both priced at around 19,000 euros.
The main difference: one roofer would use bitumen, the other a Firestone membrane. Which is better?

I have been a roofer for 40 years, and we install flat roofs with bitumen waterproofing membranes 98% of the time. I have sealed all my roofs using bitumen waterproofing membranes.