After rain, the water drains off the roof for a period of days, dripping relentlessly. I was gutterless for several weeks, and there was something wretched about working in a building that was dripping constantly along it's front edge with a muddy strip outside the door.
I didn't want to put any more plastic into the building. It took a lot of research, but I found an aluminium gutter manufacturer.
It's beautifully made, but it's not snap-together kit - you have to pop-rivet some overlap strips onto each joint with silicone bedding.
The downspout will go into a 1000 litre tank. There will be a picture when it does.