This table is SOOO great, and I get tons of compliments on it. It was easy to build as well.
I did have a problem, in that I made it to use outside and outdoor tables are shorter than indoor tables, depending on the chairs you use. I had to cut apart the legs after I had them built, which was a pain, but was completely my fault.
For an outdoor table, make your leg uprights 18-1/2" - all other leg cuts are the same.
I made mine 17-1/2" and used 2x4 material for the feet (my 1x4's kept splitting). You will also need to adjust the length of the center angle pieces, which I laid out after the legs were assembled and the horizontal supports were attached.
You can see from the photos that the unfinished legs are according to the original plan. Once the center was cut down to the new length, the angled pieces make more of a true X.
I also flipped the base upside down to attach the top. I used 2 1x1 'stringers' cut at the same angle as the top of the legs, centered the base on the under side of the top, and screwed through the stringers to the top 2x10s. I used nickels to space the top planks for drainage. I then screwed the stringers to the side legs from the side. You won't even see them unless you're sitting on the patio - standing or sitting in a chair, you don't notice them. But then there are no screws showing, nothing to patch, and it's sturdy to pick up and move.
Finished with 3 coats of Helmsmann Spar Urathane in Semi-Gloss to make it more weatherproof (water just beads off of it now - nice!)