Just a question aside.... is the purchase price really worth it considering all these obstacles? Or is it a family matter? For the demolition, you will surely have to pay more than 20,000. For the extra cost, you can usually get an alternative plot of land at normal property prices... Otherwise, don't make it so difficult for yourself, if it's all old stuff, get rid of it. General contractors will certainly increase the price if they have to build around existing buildings. You just need to have someone calculate what is worthwhile for you.