I don't know how much flavor you can get out of pumpkin itself. I did this last year and I don't know that the pumpkin did much. The pumpkin pie spices seem to be the main source of flavor/aroma.
If you've used specialty grains before, the process won't be that much different. Instead of steeping(mashing) the specialty grains for the 20-30 minutes or whatever, I mashed them for 60 minutes along with some 6-row malt and fresh pumpkin that I had baked in an oven until it was soft. I scraped off the flesh from the skin and added to the water. I can't remember, but I believe I either had the pumpkin in a grain bag or maybe I filtered it out and transferred the liquid to another pot before I started the boil.
But the pumpkin pie spices added more than the pumpkin did. I'd do more research into when and how much to add of that than the pumpkin itself.