I like the Sharon Schamber video really well except for using the OSB board. OSB does not hold up to moisture very well at all. I recommend the exterior plywood. You could also use some primer on the board that holds up to moisture and mildew. That should help prevent any problems down the road. Just give it time to dry completely.
I like the way she used cotton canvas for the top. It comes in colors and patterns in the Home Decor section at JA's if one wants a little 'bling' on their ironong board.
Thanks for the tips.