We just did a 5gal batch of pumpkin ale and very please with the way it turned out. We wanted an ale that was very pumpkin forward with only slight aromas of spices. You might be surprised to learn that a lot big box breweries don't actually use pumpkin or even puree! Super disappointing. We wanted ours to be a PUMPKIN ale, nothing else.
We used 10# of pumpkin (2# for every gal.) It produced a very pumpkin forward beer that we are exceptionally pleased with and will definitely be brewing again.
Use Jarrahdale Pumpkin (also known as Blue Australian Squash). It will be while/light blue in color on the outside, orange on inside. We scraped out the guts, roasted the pumpkin with brown sugar, and then carved out all the meat. Here is a great resource talking about roasting the pumpkin:
https://beerandbrewing.com/perfect-pumpkin-ale-recipe/
One thing we didn't account for, 10# of pumpkin added about a half to a gallon of water to our recipe. Don't be surprised if you end up with a little more than your used to.
Also the pumpkin cooks down like crazy we ended up with less than a pound of dead cell tissue being collected by the sieve.
After spilling a gallon on the floor (don't ask), and loosing over a gallon to trub (more that any other beer I have ever brewed), we ended up with less than 5 gal. going into our keg.
Let us know how the brew day goes.