For your own custom plans, head to the site and start with a satellite view of an address you enter.
It's a simple process, but I did have some trouble with an orientation marker not appearing, which is supposed to indicate which way that roof section faces.
Once you've drawn your planned array, you can see a projected output in kilowatt hours based on "your coordinates and regional characteristics such as the average weather cycle, cloud cover, surface albedo, and the orientation and area of your solar array."
Then, after choosing your energy company and rate plan (it looks like the site probably doesn't have that many power companies listed just yet), you can see a detailed estimate of what your monthly power bills would look like with the solar array in place. It digs into such things as use of solar to offset "excessive" use rates and a comparison of monthly before and after bills.
The final analysis, of long term cash flow, is perhaps the most useful.
On my mockup, it had me in the green after 13 years. After 25 years I would save a cumulative $31,521.14. That was based on a guess as to my average monthly electric bill, but I could have given specific data on monthly kilowatt usage and bill amounts for a more accurate analysis.
You can go through the full mockup without any registration, but to save your planned array you'll need to create an account with the site. There's also a Shedding Light section where you can see who has created their own mockups, in your neighborhood and elsewhere.
I can't vouch for Roofray's calculations or numbers, but if they're anywhere near correct this seems like a very useful site if you have any intentions of going solar and want to know how the numbers break down.