Parametric Slide

Customize this slide and carriage to your own specification, just 4 parameters to alter.
This is only my second attempt at writing script in OpenSCAD so still learning.
I have made a small one as a test. (see photo)
I printed the slide first then the carriage with a 0.2 mm gap which fitted okay but was a bit sloppy so I printed another with a 0.1 gap and that was a nice fit.
I would like to add some bolt holes for attaching things and possibly the option to add a locking device to the carriage, also I was thinking maybe a lead screw.

I am also new to 3D printing.... Printer GEEETech i3 (kit)..... PLA ..Nozzle size 0.3 .Nozzle temperature 200° and Bed 65° .....0.1 layer...100% infill