[Therion] Drawing tiled floor

Hello cavers, at the moment I try to draw a map of an man-made cavern. The floor of this subterranean building is tiled with more or less rectangular stone plates. These plates are approx. 50 cm wide and rectangular to the passage walls. The tiles are sometimes broken, have rounded corners, not exact the same size and other kinds of "randomness". I tried to write some metapost code to draw this kind of area fill but to no avail. Can somebody please give me a hint how to get this done? The result should look like on the attached photo. Thank you and regards, Roger