leaseback: potential pitfalls

hi, im considering purchasin a french leaseback. I am worried that they seem to be a lot of money for a relatively small amoiunt of space. does this concern any of you owneres? what do u recommend i look for in a leaseback, is it better to get one that is due to complete sooner or later? also is it true that you have to take out the mortgage before the aprtment is even built? sorry for all the questions its just ive tried to speak to an agent and they just wouldnt answer my questions atall!