Who is the owner of the site? Is there documentary evidence of their ownership? Is that evidence adequate? Is there planning permission for the house? Was the house built in accordance with the pp? Was the house built in accordance with building regulations? Are their architects opinions on compliance? Are there any tax issues? Are their any access issues?
The answers to all of these and more are what constitute good title. If you think about it logically, you cannot just decide to build something anywhere. If you ever want to sell it the title needs to be in good order.
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