This is a remix of https://www.thingiverse.com/thing:1298881
I really liked this model, but I wanted a simplified one for FDM printing. Also I wanted to add some features to make the parts more assembly friendly.
I basically "traced" over the original file in TinkerCAD.
There are pin holes sized for 1.75mm filament to keep thing aligned while gluing.
Make sure to adjust the support setting to keep the pin holes free of support material.
Rotate the middle section so that the support material is perpendicular to the outline of the shelf. See pictures.