I'm also curious as to why you would need 500. 200W seems to keep the batteries charged if there is sun, if no sun 500W won't either.
One thing to consider is that you or someone will have to get up there to maintain the solar panels and the rest of the roof gear. On my Bigfoot 10.4, between the two 100W panels and all the vents and skylights and whatnot, you have to pick your way around very carefully. 3 more panels and you would need to work on it from a skycrane.