As of August 2015, plans to build an old-fashioned farmhouse table are online at East Coast Creative, Tommy & Ellie and Our Vintage Home Love. All written instructions are accompanied by photographs.
East Coast Creative and Our Vintage Home Love both provide instructions for making tabletops and attaching them to existing bases. East Coast Creative plans describe problems and challenges the builder faced during the project. Our Vintage Home explains how to distress the boards so they resemble salvaged wood.
Tommy & Ellie's site has directions for making a 96-inch by 41-inch table. Variations for larger and smaller tables are included. Diagrams demonstrate how to cut and lay out the boards.