I modded both my Lian Li mid-towers for filters with up-rated fans.
One case uses 92x25s paired at the front the other a 120x38. I made a frame out of
aluminum angle stock that holds a double layer of home AC fiberglass filtering material.
This works very well for me. My little office is in the back of a deep 4 car garage.
The fiberglass material is very inexpensive and does a really good job of filtering with low
restriction.
Get him a case with a 120 intake, install a 120x38 because it will draw through the filter
much better than a 120x25. Even when undervolted a 38mm thick fan will pull more
mm of H2O. The filtering medium could just be taped in place.
Thin foam, panty hose and tight screens just get the chunks or cause restriction.
Fiberglas give filtering through it's thickness not just on the surface.
Consider an Antec SLK3000 for < $60.
No offence was taken...Really

EDIT: I saw Alberta and it threw me a curve.
...Galvanized