Many SUVs have roof racks - this is not an invitation to pile it on as high as you want. There are suggested limits to the amount you should load up on top. Check your manual. Also be aware that if you add weight on top, that will change your center of gravity. Higher center of gravity means the upper level weight may pull your vehicle one way or the other as it makes corners or makes any abrubt moves.
Internal weight matters too.
The cargo carrying capacity is important. Know how much additional weight your vehicle is rated - it's the payload number. When over loading an SUV that too can compromise its intended handling ability. Again, when heavier, it takes longer to make accelerations and decelerations. Watch for shifting loads as well - keep all of your cargo battoned down as much as you can.