Carrying a rifle and the ladder at the same time by himself is certainly possible, pretty simple actually. Reach one arm through a gap between rungs, sit a rung on top of your shoulder, then (with the same arm) grab a rung further down the ladder to steady it. This would leave your other arm free to carry a rifle. The ladder linked above weighs about 35-40 pounds and is only about 6 feet tall when it’s not extended and up to 22 feet when fully extended,

As for transporting it to the rally, it wouldn’t fit inside a compact car and would would be a huge pain to secure to the roof, but I’ve heard he drove a van (haven’t seen it though). Media is also saying that the ladder he bought that morning has not been found and that he got onto the roof by climbing up from on top of the A/C handler. There are photos of a ladder there at that building, but it is a 10 foot tall, orange fiberglass step ladder.

I have heard that he was spotted walking through the field with his rifle but haven’t heard anyone say they saw him carrying a ladder,