See if you can join a group tour at New Hall Mill. If not, this significant building is still worth a photo from the outside.
You'll have no end of sightseeing choices when spending time in Erdington. New Hall Mill is a good place to kick off here, but there are plenty of other worthwhile sights to experience. Bullring Shopping Centre, Arena Birmingham, and The Mailbox are close to the historic landmark and and will cap off your day nicely.