I started last night on this. So far I've been lucky, as the most tedious part has been pasting the templates (thanks to Wizard of Flight) and cutting them out. The only minor snags I've run into so far is not compensating for the lack of thickness of the posterboard in regards to the ridge that runs around the helmet below the dome and also the dome base and the rear support beam hitting the back of my head so that my nose hit the front of the helmet.
I solved the first problem by unsticking the support beams and resticking them slightly squished inward so that there was a gap between the outer edge of the beams and the lip of the helmet. The second problem was solved simply by shaving the rear of the dome base and rear beam a bit.
Since the posterboard is slightly flimsier than cardboard or the other materials people are using to create their helmets, I had to leave 2 supports connected in the shield part until I stiffen up the inside with spray can rubberized undercoating later tonight. I think the minor flimsiness has actually been an advantage to work with, especially in the cheek portion. I've been using scotch tape to hold everything together, white glue over seems, and rubber cement to hold the templates to the posterboard. To cut everything I've used sharp scissors and an exacto knife when necessary. I did use regular beer box cardboard for the dome base and supports.
I'll give some updates if anybody's interested. This is a lot easier than some might think.