George Washington, Thomas Jefferson, and Ben Franklin are all believed to have brewed beer with pumpkins. Beginning with Buffalo Bill's, pumpkin ales have been a fall staple.
But, for homebrewers, pumpkins aren't easy to work with. They're mostly starch, so they need to be roasted, and even then can gum up the works - and, they don't taste like much on their own. When most people think of the pumpkin, what they taste is pumpkin pie, so they the beers usually get a generous portion of spices like cinnamon, ginger, allspice, cloves, and nutmeg, which can be tricky to make balanced and not overpowering.
I make mine with canned pumpkin, so that it's already pureed, baked to break down the starches; and with an infusion of spices made with dark rum rather than vodka, to capture the volatile essences of the spices as well as the molasses character of the rum.
Mash8 lb domestic 2-row
1 lb domestic Munich
1 lb red wheat
0.25 lb Special B
0.25 lb Belgian biscuit
0.25 lb English brown malt
Other fermentables3 x 15 oz cans pumpkin cooked 45 min @ 350F
Hops1 oz Mt. Hood 5.4% AA @ 60 min
0.5 oz " @ 20 min
0.5 oz " @ 5 min