Wifi repeater

Your metal building is basically a faraday cage. You'll need an antenna outside of it, ran to a wifi client device inside. From there into a switch for wired devices, or an access point for wireless.
Cable underground would be best, but I see that's not an option for you due to the concrete. By the way, if any of you do this, get shielded cable, and ground it.. a lightning strike that hits that wet ground will give you a bad day if you don't. I have a cable run to my garage this way.
Microsoft Certified Systems Engineer since '99.