I've started tweaking my design to try and save some pennies without compromising too much. Our proposed kitchen is north facing with a 2.7m French door with side lights for the exit into the garden. The kitchen length was 7.2m, but I've reduced this down to 6.2m. As this now means a shorter flat roof, approx 2m, would keeping the two skylights we had planned add enough light to warrant keeping them?  

 

6.2m feels too long for just the French doors to provide light, but the skylights might not provide enough light to help.  

You could also put the openings and upstands in, then cover over with the roofing material. Gives you the option but saves money upfront.