I am in Northern California near Sacramento. I'll probably do some real small scale testing tiles first so as not to "contaminate" too much clay. I'll make tiles of the same size/dimension and each tile will have a different measure of coffee in it. I'll see how well they dry .. .how they stand up to firing, what kind of strength and porosity that they have. If anything looks promising, then I'll try to build some structures to hold water. If you have ever worked with clay before then you can understand how it can be a messy process. I'd imagine that once the wheel and water got exposed to coffee grinds then it'd be difficult to clean up the mess. I'll test on a small scale first. . . .because my studio is always immaculately clean-lol. Sounds fun though. Firing will be with an electric kiln. Someday I plan on building a wood fired kiln . . .and then it's going to be a choice for the wood around here between heating the house, building Hugel beds and feeding the kiln. I already know that feeding the kiln will win out every time.
Put on a jacket if you are cold kids!!! Hugel beds are cool but . . .firing the kiln is way cooler than that.