I am setting up a WiFi connection from my house to a metal shop. I plan to have an AP outside the metal building connected to another AP inside the building. The inside AP is intended to support connections from within the building. The metal building is 4800 SF with no internal obstructions (ie; open space).
My question is: Will the inside metal walls cause problems using WiFi inside the building? Since the walls are metal, will signal reflections cause so much RF noise that I won't be able to use an "in building" access point?
You should experiment with the placement of this inside AP.
IE in the exact center / one end the corner where you will need it the most.
Also if it has scalable power settings I'd experiment with that as well. Sometimes cutting back power can help with reflection and noise issues.
Also using a narrow beam panel antenna instead of an omni mounted at one end of the building might work out the best.
Picture a flashlight beam at one end of the building shining strait towards the opposite end. it gets weaker with distance, but still gives some light on each side along the whole path and is not strong enough to reflect much . It doesn't have to be mounted directly at the end wall 30' or more feet away should still give a reasonable connection behind it. Experiment with it.
Even a reflector on an omni could provide similar results.
I might suggest using 802.11n equipment as the metal walls will give you significant multipath reflections irregardless of the antenna style. 802.11n is designed to use that to its advantage whereas 802.11a/b/g is extremely hampered by that phenomena.
As for antennas then I would just try using omni's fist to see what the results would be. directional antennas are going to have areas of weaker coverage. I also would suggest staying with enterprise equipment such as Cisco, Aruba or Meru. They all have good 802.11n devices.
Keep all your antennas polarized correctly, for vertical dipoles, that means straight up and down. The reflections bouncing around inside will be out of phaze and polarity with the direct signals, and won't interfere as much if the antennas are polarized with each other.