I have been looking at redoing my table & have seen several designs for it. I liked Allted's simple design, so I made an openscad file for this using the dimensions of my table to get a visual of what different sizes would look like. I have set the default size to the size of my table which is 4'x3'x30". It should be easy to figure out what each variable is, but some names may not be obvious until you change them & see how the model changes.
Be sure and check the dimensions before cutting any wood to make sure it looks like you want.
Rev2 - revised for Quantity of Top Ledge Lengths if only 1 middle stiffener used.
Rev3 - Legs, Top Ledges & Shelf Ledges can be different Widths & thickness now
As I was building this table, I realized 2x3's for the Shelf ledges should make it just as strong, but give me a little extra shelf height & be slightly lighter.
Rev4 4/8/2016 - Display Shelf Usable Heights with a visual cube for each shelf
Let me know if you have any problems with this.