Mine's low tech and inexpensive. At my location, we don't get rain often. My roof has 14 scuppers. Under each scupper, I position a 30 gallon bin (the ones designed for trash), with cover.
When rain's in the forecast, I remove the covers to hopefully fill the bins.
Distribution is another matter. I thought of ways to pump the water out or use gravity. Then I quickly realized that as I devise more ways to make my tasks easier, I get sedentary, old, weak, decrepit, and start to feel the earth's gravity getting stronger. So I use 5 gallon buckets that I fill to about 2/3 (too much and water sloshes out) and carry the water to the plants. Right arm on one trip, left arm the next trip. See if I can get to a plant without lowering the bucket to rest, and using controlled movements such that no water spills. Desert plants do not need frequent watering so I stagger the watering schedule.
Main problem with this system is if a bin is left uncovered and the surrounding area has dried out, I sometimes find a squirrel swimming in it, unable to get out. Darwin was right. As easy as "shooting fish, er, rodent in a barrel" is, I don't do it. The thought of blood-borne pathogens is disgusting, even though it's likely the rodent has contaminated my rainwater with waste. I've tried electrocution but it doesn't work since the GFCI trips. How do they do it in the movies,
hair dryer in bathtub?