Did a little bit of modelling using Draftsight to rough things out and also had a little bit of a play in OpenSCAD.

If I can make OpenSCAD do bridle joints it could be a nice way of modelling the desk.

All elements are 2x4's (35x89mm)

Internal space is 935x450x600mm which is sufficient for a 21u 4-post 19" rackmount setup.

If I get a chance I will include the double angle rack rails in the model.