The rails underneath look like they are about 1 1/2 inches high and about 5/8 inches wide. Didn't measure the length of them. Far enough apart to fit over most ironing boards - maybe two inches in from the edge.
There are three boards underneath - one on each side and only one at one end. Seems to be some kind of smooth hard-wood. I don't think it's pine. Not oak, either.
They are nailed together at the end, but I'm not sure how the rails are fastened to the large piece of plywood. Maybe glued? I didn't feel any screw or nail holes when i went to look at it.
The only "finish" the woods have is being sanded very nice and smooth.