Here is a simple way to built a solid desk to fit the dimensions you need.
Step 1: Design
First thing is to determine the shape and dimensions of the desk. I use 3D drawing (SolidEdge in this case) to determine the dimensions of all the parts.
Step 2: Prepare the Material
Once the drawing is finish. I cut all the material needed to built the frame. I took 1/8 x 2 x 2 tubbing and angle corner. I also use flat bar to joint the desk tops together.
Step 3: Welding Time!
The most important thing before I start the welding is to clamp the pieces strongly on a straight table. The heat produced by the welding tend to wrap the metal.
Step 4: Finish on Frame
I use a metal brush mounted on a grinder to remove all the black and the oxide.
Step 5: Fixe the Table Tops to the Steel Frame
To keep it simple, I buy the bamboo table top that are almost the size that I needed. It is 1,5 x 26 x 72. I just have to cut the length. You must drill holes before apply the screws because bamboo is a very hard material.
Step 6: Finish of the Table Top
To finish the top, I use natural oil.