Shadows are your best comparison for size differences. If you can find something with one of the small house shape buildings below the tower and calculate the average house heights followed by the shadow measurement of the tower or traveller in comparison to that then you have your size. Going by measurements of a skyscraper is probably unwise because they're often far different from One another. And who knows of that was one of the ones trying to be the tallest on earth. I'd go by a house down below since those generally don't vary much on average in height. For the width of the outer shell wasn't it damaged and broken? Shouldn't you be able to use your height calculations and apply them to the shells width via the giant chunk removed exposing the innards of the traveller? You ought to be able to calculate the inside density but if it really weighs that much it probably has a super dense core like all planets, stars, moons, comets, asteroids, and other body's of space so if try and configure that as well. Also there may be antimatter involvement or antigravity as it manages to get hovering just above earths surface without crashing into us as gravity would like. Just to travel and not throw off other body's orbits or crash Into anything presents some questions and problems that would need working around.