Because we were putting our new table cover over our existing table, we needed a rim that would hold it in place that was made of 1x2's. The 1x2's are an inch and half wide so adding two of those adds three inches overall to the length and width. I also added an extra 1/8" overall to both the length and the width so that there was a gap underneath so that the table could easily come on and off.
After all slots are cut, stand each board on end and coat the edge of jointed side with wood glue. Next coat the biscuits with glue. Insert biscuits in one side only of each board, then insert glued biscuits in the empty joint of the next board. Assemble planks in order until the top is complete. Don't worry about small gaps. Next, carefully lay the top down and attach pipe clamps at roughly 1' intervals. Slowly tighten each pipe clamp in a consistent fashion until the gaps disappear*. Small amounts of glue can be removed when dry; scrape up any puddled glue with a plastic putty knife. To minimize sanding later, avoid working glue into the top of the wood. Let the top set overnight.