haha , I had a client tell me that I should use a drone to take pictures of his sign and get measurements. I told him that sounds fancy and all but I prefer to use subtense method and I can tell he didn't do well at math. Simple put it is a measure of known distances to extrapolate what you are measuring.
You need to also get a survey paid for and get real measurements, evaluate the structure, electrical etc. of hire someone who can do this for you.