One saving grace of a flat mate is setting up 'family sharing' on each other's Steam libraries at the earliest opportunity. Another saving grace is leveraging local network game transfers to then have a go at whichever game has become your roommate's flavour of the month, and judging them accordingly.
Recently though, Steam's local network game transfers hadn't been working as intended. For instance, some folk would attempt to kick off a local transfer, only for Steam to download via the internet instead. That's less than ideal if your bandwidth is scarce or you're working with limited data. Thankfully, Valve shipped a fix to the stable channel of the Steam Client on Monday.