IF two 100W panel were much cheaper (15% less) than one 200W panel, would it make sense to purchase them? Or are you asking for twice as much trouble with hooking them up and purchasing the mounting racks? But a benefit would be that if one went bad you would be able to replace it much cheaper.

Also, I was wondering if you had the space, wouldn't inefficient panels be a better choice, because they would cover more roof and thus reduce the heat gain of your house?

As everyone can tell, I'm new to this, so any help is greatly appreciated.

In the end its all about the cost, what ever in the installed system provides the lowest cost and works for your application.

Two panels vs one panel may have higher mounting hardware costs.

Two panels may give you more voltage options

Two panels are easier to manage by yourself for installation

Lower Efficiency panels will cover more area and they do somewhat lower roof temperatures. I have found that the solar panels heat up and they still radiate the heat back onto the roof as a guess, maybe a 50% reduction if you have a 4" air space. The smaller the air space the higher the IR transmission from the panel to the roof

As you will find as you move forward into you solar project, there is no right and wrong answers. It all about what works best for your application and your budget.

I always recommend people consider factory seconds, like www.sunelec.com sells, that is usally the single biggest savings one can do for a system without effecting the harvest capabilities.

Ditto what Solar Guppy said.