I cut and bent the sign in such a way as to try and capitalize on the inherent properties of the material, namely its tensile strength. Since I designed it as I went along, the substructure is a little weird. I just kept adding pieces until it stiffened up. With a little more forethought, you could organize the structure better, but I kind of like how it developed organically, and the final form reflects that.
That said, it is still surprisingly flexible, and conforms to your body some when you sit in it. At about 13" off the ground, it is a low, lounge-type chair. Given that the wood is already weathered, and the sign was meant to be outside, this chair is great for a porch, patio, balcony, or deck. Originally 2' x4', the dimensions aren't ideal for a chair, in that the seat pan is a little long tailbone-inside-of-knee wise. However, when you sit in it, the big 45-degree cutbacks on the front edge are where your legs go, and it works out fine that way. It is really comfortable and incredibly lightweight -- you can pick it up with one hand.
I don't expect you to find the same sign, or the same dimensioned sign, so I'm not going to include any dimensions. In true readymade style, I measured everything just by holding it up and eyeballing. You can do the same . . . .