I made one for my car out of an ebay catch can and some metal filter mesh. Made a seal around where the top bolts down with some Loctite 5910 - left over from doing the rocker cover, then placed a sheet of filter mesh between and cut to shape. Also made a feeder tube for the inlet pipe to go through the mesh to make sure the maximum filtration takes place. also added a finer mesh over the outlet to make sure everything was picked up before going back through the throttle body
This was before i added the filters to the can - was in use for a couple months, about 2k miles
as you can see both the outlet and inlet had mayo on - the pipes were just as bad
Gasket around top of catch can
Breather pipe on inlet, mesh on outlet and gasket around edge
Main filter mesh fitted - also added some loctite to around the inlet pipe to make a seal between the mesh and the pipe
Finished article
Can fitted - AFAIK gen 5 and 6 engines run slightly different crankcase breather pipe positions, but as mentioned just take that pipe out and replace with new hose with catch can in the loop
After checking the can a couple of months after adding the filters, it was a ot cleaner and the outlet pipe was nice and clean
Think total cost was around £45 - 25 for the can, 5 for couple of different grade sheets of mesh, 10 for new hose,5 for some jb weld for the pipe...