I built a "raised" bed this year but all I did to raise it was till a large area and then shovel out some walkways and pile up the topsoil from the walkway making raised beds. The beds are about 8 inches higher than the walkway. I have various shapes and sizes but the one I put pumpkins in was only about 3 feet wide and about 15 feet long. Three feet was not nearly wide enough. Early on I could see roots from the pumpkins coming out the sides of the raised beds and the plants were right in the middle of the bed. If you have the space I think you should try to make the beds five feet wide. Although you might not have the problem I did since it sounds like your bed will have actual sides not just mounds of soil. Another thing to consider is the pumpkins probably won't stay confined to the patch, mine certainly didn't but I just let them sprawl into another bed with corn and out of the garden. Even though I feel the beds should be larger I still have two pumpkins on each plant and I only fertilized maybe four times so clearly raised beds work fairly well. Since, as you know, pumpkins love space I think you should try to make the beds as wide as you can safely weed the soil.

Also I thought you should know my beds are flat on the top and the sides are as vertical as I can make a pile of dirt. But the thing I think helped a lot with the raised beds is that I made a nice lip around the edge of the entire bed so that when I watered them the water waas forced to stay in the bed and not run off into the walkways