Here is how I do mine. Sam's club, in my area anyhow, has whole pork butts for a reasonable price--two large pieces, 20 pounds or so total.
Start this recipe the night before you plan to serve it.
I mix up a cup of brown sugar, a tablespoon of salt, 2 tablespoons of chili powder. Rub this all over the roasts. Feel free to add or subtract ingredients--sometimes I use packaged steak rub or sate seasoning instead of the chili powder, but IMHO, the sugar is a must. Add cayenne for some heat, if you like. (The crust on the roast will not be very sweet--most of the sugar caramelizes.)
Put both roasts on a rack in a big pan--line it with foil to make cleanup easier.
Preheat your oven to 400, put the roasts in and immediately turn the oven down to 200.
Wash the dishes, watch some TV, go to bed. Wake up in the morning to the most wonderful smell, but don't eat it yet. (Well, you can pull off a few shreds--no-one will know.)
An hour or so before you are ready to eat, take the roasts out and pull them apart with two forks. You will be cooking this roast for 16-20 hours, depending on whether you are making it for lunch or dinner.
I make two because it freezes very well, and works in lots of recipes--enchiladas, tacos, sandwiches.