That many owners of travelling vehicles are fighting the weight with too much load is pretty common. That even travellers with Roof top tents have to take care, is less known.
Not all cars are able to carry a roof top tent (RTT) under offroad conditions. Because the offroad calculation change the bill.
Here is the calculation for a Ford Ranger Ute: 75 kg roof load capacity, 50kg on-road, 33.5kg offroad allowance.
Even for on-road trips you have to choose your RTT wisely to staying legally, the most roof top tent are above 50kg. Details of the calculation with the weight of different RTTs and diffrerent roof racks you find here:
Roof load weight and the roof top tent - [Leaving Land Cruiser Club]
I try to collect the calculations for different cars and models together at the same place.
Please consider the weight for your Buildup at a early planning stage.