The nice thing about this project is you can build it to your exact specifications. We have a fairly small dining room, so I went with 36 1/2"x60" and 30 inches tall. You can go longer, shorter, wider, whatever you want. So the first thing you have to do is decide how you want this built. Decide the size, shape, finish, and type of wood before you start.
I built mine out of aspen because it's cheap, easy to work with, and fairly cheap. You COULD build the entire table out of construction grade pine for around $50, furniture grade lumber will run about $120 and up depending on what kind of wood you choose. It's whatever you want to do. Just keep one thing in mind, pine is very soft wood. Writing on the table, dropping things on it, etc. will dent and scratch it fairly easily. If you're OK with this and you like the knots, go for it. Some woods won't take stain as well as others, some are harder to sand and work with, and you may think some wood is just plain ugly. Do your research.
UPDATE: I built a matching console table for the dining room. Find it here: http://www.instructables.com/id/Build-a-dining-room-console-table-side-or-serving/
Step 1: Make the legs
My legs final length are 29 1/4" long. I start by cutting 4 1"x4" boards to 36" long FOR EACH LEG! You will have 16 3' long boards total when you're done. Now, you'll take 4 of them, lay them out and glue them together using wood glue. Don't be shy with the glue, if you don't have glue splooge out when you clamp it, you aren't using enough. You'll have four 3 1/2"x3" table legs when you're done. We will cut these to their final size once the glue is dry.