I built mine out of two pieces of 12 inch by 6 foot soft pine glued together and have four braces screwed onto the bottom to keep it from warping. I ran my board through an over head sander until it was level then a plainer, it's very flat. I mostly use pins or weights so it has served me well for about 12 or 15 years, been a while. I have removed the bottom braces a couple of times and resurfaced it over the years. Didn't need to but I go over it with a filler then resurface it to remove any nasty old epoxy and glue. Old school but it works for me.