The roof section is my only concern & I know that's where to start. I'm wondering if I could lay it on its side & secure it somehow & pop the top out sideways.
Most manufacturers will tell you to start with the sides, then do the roof last. Personally, I have done it both ways. Whichever is easiest for you. Can you lay it on its sides - sure. You may have to decide if its easier to do the roof first, then start pulling the sides out, when done, just flip it upright.
Just watch whichever way the wind is blowing so it doesn't turn into a sail.