Most actual roofs have gutters. These will be attached to a drain down the side of a building. It wouldn’t be too hard to drain this into some kind of container. From the coding point of view you’d check to see how many roof and wall tiles it’s attached too.
In a survival environment using raincoats, ponchos, canvas, or maybe event tent roofs for this would work too.
This is normal where I live. My parents’ house has a couple of big tanks to hold the rainwater coming off the roof, and that’s the water supply for the house.
Raincatching could also be done on the roof of a vehicle and run through a filter.
this have more sense than creating farm of galon jugs with funnels
Depending on the drainage and the abundance of rain every pit might fill with water irl.
So if i have suitable ground i wanna be allowed to make a moat :S
edit: we d need water physics for a satisfying system … whcih is quite hard i would asume.
yea, water physics will be relay hard in turn based environment what is additionally 2D what makes it much harder
Water physics in DF are really bad because it runs forward at a constant rate. I often take ten seconds or more between ticks. Also, you modify the world much less in CDDA than in DF, so it’s possible that DF-style water physics won’t be that bad here. And, if you want to get crazy, you can pre-calculate future flow during time between turns when something happens to change it, under the assumption that those changes are rare. But that’s getting squarely into premature optimization territory.
I’m not even going for water physics. 
Just an easier way to gather water then having a really high construction to get yourself a water source.
Have you tried a funnel (not makeshift or leather, the real deal) over a 30 gallon drum?
Last time I did, it filled the entire thing over the course of two rainstorms.
getting water is realy easy thats not my concern either
I want a moat >_<
If you can fill a 30 gallon drum that easy they it’s OP as heck.
it depends on how long it rains, when i was using funnels it taken more time to fill a galon jug left alone whole barrel
Retroactive rainwater collection was broken around 0.C, meaning you had to stand near the funnel (less than about 60 tiles from it) for it to work.
Drizzle fills funnels at half the speed of rain. Storms are the same speed as rain.
Proper funnels (not makeshift, not leather) are 20 times better than makeshift and leather ones. Yes, 20 times - not a typo here.