We needed a sturdy table but didn't want to spend a fortune buying one so decided to take a stab at building one. Our space isn't too large but also wanted the ability to expand the table with leaves if we have a large crowd. I built leaves by cutting notches in the horizontal leg 4x4 and then sliding in/out with 2x2's attached (see pic).
I will say it makes life a whole lot easier learning how to use Sketchup or some other design software. That way you can visualize what it will look like, cuts you need to make especially if you will be deviating from the original post design and don't want to do math in your head (like me).