DH and I own a flat in London. The only other remaing flat in the building has come up for sale (for the first time in 10 years). The two flats are in a detached building on a fairly big plot of land - both flats have a large garden. We are in the very early stages of looking into buying the neighbours flat, and subsequently the freehold, with a view to getting planning permssion for the site. We would then either sell the site on with planning permission or (possibly) sell the flats (without smaller gardens at present) and use the money to self build a house in what is currently the back garden. We need advice on what could be bulit on that plot and what we coudl get out of it before we commit. This is a once in a life time opportunity for us. WHere do we start?