Yes, you can use Halo even if your home (or any other building you frequent) has a metal roof although it can affect the collar satellite reception more than a non-metal roof.
If you are inside of your home or any building with a metal roof, the Halo Collar will detect that it is indoors, which will put it in "low GPS" mode, pausing navigation and fence preventions. This is normal and expected performance for the Halo Collar. When your dog leaves the house/building and goes outside, Halo’s GPS receiver will quickly switch to "Strong GPS" mode and resume navigation and fence preventions.
It helps if the collar picks up low-level satellite signals when indoors though to help with its general accuracy when going back outside. If you notice in the GPS signal settings that the collar is consistently showing signals under 100 when indoors and off of your dog/on the charger, then it may help to move the collar to a different location. Try placing it next to a window or an exterior facing wall or door.