They're all over the web, some folks being informative others selling you their guides and materials.
If you need a really odd layout, it might be worthwhile. But if you can use a conventional layout, consider: You've got to solder ribbons front and rear, interwoven, on every panel. You've got test every panel as you add more. You've got to somehow SEAL all those panels in between a tempered glass sheet--of the right kind of glass--and the right backing, which needs to also be an insulator. And then frame it all so it won't stress or crack. There's a LOT of handwork to be done and at that point, you might as well gamble on the cheap
panels being marketed by all sorts of no-name shops.
Unless, of course, you need some really odd shape.