Wanted some solid reusable seed trays, so I modelled this 4x4 design. The large drainage hole makes for an easy removal of the plug when it is ready for transplanting. 

– Tray Size: 141mm x 141mm x 45mm

– Cell Size: 30x30x45mm

– Drainage Hole Diameter: 15mm

Added an optional bottom tray as a separate print profile if you want to catch any excess water.

P.S. I also made a iPhone app for this kind of thing, To Grow, a simple garden journal for photographing your seed packets and tracking what you plant through to harvest. Feel free to check it out on the App Store!