Currently I don't have one, but they are fairly simple to construct. You can buy premade models if that is your preference, but making your own is much more fun and encouraging. Here is a good site to see all the basics for pumps, valves, line/hose, reflectors, etc. It has plenty of illustrations to help better understand. The end product of these is sustainable hot water without the need for boiling small amounts at a time. If I were to make one, here's what I'd do:

Supplies-
30 gal food grade plastic barrel
55 gal steel drum
lumber for framework
2 x 20' 1/2" black garden hose
solar fountain pump 1/4 hp
60 psi pressure valve
toilet style float valve

First, paint the outside of the barrel a dark color like black, dark green, or dark blue. Build a support structure inside the drum for the barrel to sit. This will be the core and shell (barrel inside the drum) which can be insulated to retain heat while absorbing natural heat from the sun. Build a support frame for the drum where it will be mounted (preferably on the roof gable as to take optimum advantage of gravity for your natural water pressure). The barrel should have 2 or more fittings on the lid. Attach a 20' hose to the barrel and run it out along your rooftop. Add the solar pump here to circulate the water all day. Attach the second hose to the pump and run it back to the barrel, where it is also attached to the lid. This is your circulation setup as well as natural solar heat. Variations of the hoses can be from just straight hoses, to being coiled and mounted on a metal plate. The choice is yours. Now that the circulation part is set up, we can move to the refill. Depending on your preference, these can either be filled by hand pump, or by a float valve inside the barrel to maintain a constant water level from your existing water source. Just like the float valve in your toilet tank, it needs only water pressure to run. You can run a 1/4" or 3/8" line from your house water to the valve so it stays topped off. Using a small hose here prevents a rapid cooling of the barrel water inside. The pressure valve goes from the barrel to the exterior of the drum. This is just a preventative measure to keep the water pressure level safe. Another hose with a valve setup on the end can be used as a faucet-type supply to you.
Operational overview - Once completed the float valve will allow water into the barrel. The solar pump will circulate the water during the daytime sun and raise the temperature. As the water is used, the float valve drops allowing the tank to refill as needed. The heated water remains in the barrel overnight while being insulated by the fiberglass batting between the barrel and the drum. It starts over the next day.

Another big option is to hybridize the solar setup with your existing water heater. This calls for a good deal of plumbing and valving, and is not recommended for the beginner. The link above shows how complex it can get. But for sustainability, my plan will work. If you have a spare water heater tank, you can use that to store more hot water inside the home. It will take some modifications (removing the elements, valves/adapters, etc) but can double your hot water capacity. On this setup you can add an additional solar water pump/hose assembly to the water heater tank to continue circulating the inside water through the exterior unit. Make sure this pump has an equal or lower capacity than the rooftop pump to ensure a more controlled water level. Or of preferred, the rooftop pump setup can retrieve water from the rooftop tank and circulate it down to the water heater tank, and back up. There are numerous possibilities to set this up. I've provided only the fundamental info and the end product is whatever works best for you. The fountain pump is better than a regular water pump as it is designed for continuous runtime (provided the bearings stay cool). This is why you get a bigger pump than you need, therefore putting a much more reduced load/burden on the mechanisms. This allows it to run longer and more efficiently. The options are pretty much endless for making solar water heaters. The only limit is your imagination.

That's about it for this thread... see ya soon!