the "box" is a transformer.
Primary single phase electric runs from the nearest pole to the transformer. A "secondary" service line already runs from your "transformer" to your house. All bge needs to do (assuming there is no natural gas involved) is run another secondary line from the transformer to the new house. it will be 3 feet deep , and the trench they dig will likely be only 18-24 inches wide. The utility contractor is then responsible for restoration( grading and planting of new grass). Most times within a few months you cannot tell that any work has been done.
Typically a single tranformer will serve 1-6 homes, depending on how many amps service each home has, and the distance from each home to the transformer. In planned new home development construction the transformers are insalled within the existing utility easements, and typically on a property line(half on his and half on yours). Within a utility easement Bge and local public works has the right to do what ever they want regardless what you may think. They can dig in water and sewer, install gas mains, oe even widen the road 40 feet into your yard. Why isn't your transformer within the existing utility easement?
I worked as an installer for BGE for about 5 years. If it was me, i would do the neighborly thing and let the home owner run a service.If it was a builder , building to sell for profit, i would charge him some $$ for the right. I'm 99% sure there is another way to run the electric without coming onto your property, it would just cost the builder more money to do it. Before you sign anything take the document to a lawyer and have it checked out, and make sure you arent giving the person a right to do anything else, like install a driveway or move the property line. If you can't afford a lawyer, offer to sign if they reimburse you for the consultation with one.
Good luck, if you have any more questions i still have contacts in the industry.