when your house is built, someone from the office comes, surveys your house on the property and gets paid for it. Sometimes it's called Katasteramt, sometimes Vermessungsamt, you name it. The data can then be viewed later or are available online. I still don't understand your problem. Your property is forest. OK. So most of it has to go anyway? Then it's enough if you say to the meter up to where he can fell, the rest stays standing. I would save the money for an external surveyor.