In all major campaigns you see politicians using corner lot or major intersection signs. These vary in size from 2 X 4's to 4 X 8's. For the purposes of this paper, let's just refer to them as billboard signz.
Just by their size they say, 'hey, this person is important' People just aren't used to seeing individuals in advertisements. The one exception being a major star. Obviously, that's not bad company in which to be viewed!
Regardless of what material a person might choose to make their billboards, they are going to need massive support. This is why it's really not necessary to use heavy duty, 10mil corrugated plastic. Standard four mil. can be glued, stapled, nailed, screwed or bolted to affordable plywood. It's light, easily shipped and easier to handle for installs (especially if you need to attach it to a fence or building face). Because it isn't so porous, it prints more beautifully than wood. It will last longer and it doesn't require you to have an artist on your staff.
One of the saddest things I see is a candidate spending a fortune for great print ads, flyers, trinkets and yard signz, but trying to paint their billboards by hand. They look cheap by comparison. Because they are so visible, they make a person's entire campaign appear cheap, like it's on its last legs. With what large, corrugated plastic signz sell for these days, there really is no excuse for this. Spend a few extra bucks, save your volunteers a whale of a lot of time. Buy professionally lettered or screen printed billboard signz. You'll be glad you did.
Need to save a little more? 4 X 4 signz have the same basic printable area as 4 X 8's. The larger signz just have more blank space. 4 X 4 and smaller signz can almost always be shipped via UPS or FedEx Ground as well. Personally, I like to see people use 2 X 4 signz. They can be supported with just four standard yard sign stakes! They can be printed on both sides easily and affordably for best visibility. Perhaps more importantly, they don't tear up supporters lawns like large posts and one person can put up dozens in one afternoon! With the savings, you can buy a lot more signz to make more impressions.
More impressions or a greater impact, the decision is really yours. Either works well, with different types of campaigns and locations. Certainly, any campaign, county wide or greater, needs them for their candidate to be taken seriously.