This is a jumbo-sized version of https://www.printables.com/model/57885-self-watering-rectangular-planter-with-optional-la that I created from scratch and using the original model as a reference. The main change apart from the size is that I added a cap for the water column which was a common suggestion shared in the comments section. Otherwise the assembly works the same as the reference print that this remixes so I'll defer to that page for details.
The inner shell which is where you'll be placing soil and plants measures 218.00 mm length by 190.00 mm width by 119.00 mm height.
The outer shell which will guide where this fits measures 246.00 mm length by 202.00 mm width by 162.00 mm height (all the way up to the water channel).
The outer shell, the floater, and the floater indicator were printed with waterproof PLA settings at 0.15 mm layer height based on https://blog.prusa3d.com/watertight-3d-printing-pt1-vases-cups-and-other-open-models_48949/. The other parts were printed at 0.15 mm layer height and otherwise default settings. The shells were printed based on the Speed preset whereas the other, smaller and more detailed parts were printed based on the Quality preset. In hindsight I think the inner shell could be optimized by using a larger layer height; the inner shell doesn't need to be waterproof so those settings aren't as important.
I did have success using PLA for the floater in spite of the warnings from the reference print. For me the key was to keep it completely hollow.
I finished all the waterproof parts with controlled, quick bouts of heat from a heat gun which several commenters suggested helps the waterproofing by essentially melting together inevitable small gaps and imperfections. I haven't suffered any leak thus far.
Please reach out to the author of the original model if you would like to use this for commercial use. https://www.printables.com/model/57885-self-watering-rectangular-planter-with-optional-la
The author marked this model as their own original creation.