Lex, I'll say it again - stop thinking. Start doing. First things first (inverter isn't "first"). Take a measuring tape and go on the roof, see how many 100W or 120W, or 140W panels you can fit. Then start a new thread like "what controller for me, what wire gauge" etc.
Like Don said, big 24V panels are cheaper per watt, but they are usually 200W or larger, they are heavy enough to need a second man to lift them onto the roof, and they require more expensive controller (which is usually more efficient as well).
First things first.