It should be noted that the 400 feet above a structure rule only applies in class G (uncontrolled) airspace. If you need a LAANC, you have approval for a fixed AGL based on the grid number. If you want/need to fly higher than the grid number you can request that clearance through extended LAANC or drone zone. Also, if the structure is critical influence (CI), you may have further restrictions. In Nevada you have to remain 500 feet (horizontally) from the CI unless you get approval from the CI owner (which you probably have if you are working for the CI owner). Without that approval you can't get within 400 feet of the structure where you can start going up to 400 feet above the structure.