I designed this for my Mendel90, but really it can be used for any printer.
There are times where I want to purge the old filament out and 'start' the new filament through the extruder, but I don't want the extruded filament to stick the heated glass bed. I came up with this "purge pan" based on designs we use at work (I work with plastic injection molding) where these types of devices are quite common.
The idea is you'd place this purge pan on your print bed and purge the old filament along with the new filament into the purge pan instead of on the heated print bed. The small footprint of the purge pan keeps it from sticking to the heated print bed.
I printed mine upside down, thus explaining the nasty appearance inside the 'bowl', but its purpose is just to collect purged and wasted plastic, so it doesn't need to be pretty.
I did not print mine with supports, as it doesn't matter for its end purpose, but supports would help make the pan look better.