Rectangular Gutter Cover for a common application in wet room drainholes (DE:Abflussrost)

Untested first iteration of a parametric design.
As si the lid has 142mm square dimension and the seat area tapers down from 136mm square at the top. The total Thicknes is 20mm. You might get far adapting the design using scale functions of your slicer.
I can make custom versions for you at a cost, or might sell the parametric model at a site to be determined...