FM signal in metal buildings

Has anyone here solved the problem of getting a good radio signal in a metal building?

Yes, download the app for your favorite station on your smart phone, plug your phone into your radio/stereo jack, as long as you have wifi or 3G you got your station

I have been doing that lately, but need to setup a repeater or signal booster because the internet comes into the house and the shop is at the far end of the signal range.

Most of the basic plug in deals work as repeaters. I have a cheaper unit 40-50 bucks or so and it works ok. My parents have the apple airport, it's flawless but double the money.
Another option is if you can move your router closer to the shop. I've seen some people put tin foil and other crap behind the routers to try to reflect the signal. They claim it works but I had no luck with it, that's why I got my router/repeater

Use a short antenna mast outside the building.