Evaluation. Step Two.
There are many things you're going to want to look at when you're evaluating the construction of a solar electrical system. Here's a checklist:

1. The service connection.
What is the difference between busbar rating and main breaker rating? This could be the difference between being OK, and needing a service upgrade.

2. The roof support
As a fact of life, houses built after WW2 and before new building codes required roofs to be more strongly enforced tend to require additional support to handle the weight of a solar electrical system. Factors that come into play are roofs that have additional layers of shingles, ones that are particularly long in span, truss roof systems using only 2x6 beams, and roofs with 24-on-center spacing for rafters.

3. Panels
Maybe you have a tree in your yard. Or that there is an obstacle on the roof, such as a vent pipe or a skylight. How do you find out about how many panels you can fit? The only way to find out is to have a harness on, walk around up there, and measure the thing out. Any company that says they can determine from outer space how many panels you can fit on your roof is overestimating the power of their computers, and underestimating the validity of a hands-on experience.

4. Conduit Route
Lastly, determine the route of the conduit, from the rooftop to the main service panel. Solar electricity must be housed in metal raceways indoors in order to meet with NEC Code.

On to [system design]