[santiago]

Hi Quentin
Have a hunt round the area then try and get an idea of plot values
work out your building costs, architects, solicitors, land investigation & survey costs, etc add it all up then compare it to your estimate of completed project values, get the lease checked to see if it included the land when leased to you then make an offer based on your sums
if the land was leased to you as part of the property, then it isn?t really worth much to the owner for another 70+ years, so bear that in mind before offering, get your solicitor to check it out then you'll know.

Good luck
Santiago