Hello, I'm adding a outdoor subpanel to my new Metal building that is about 50yrds from the main breaker. My main breaker is a 200 amp main lug. What time of wire do I need to make this work? Plan to have 120/240 machine inside this metal building. Thank you.

You can use steel, aluminum, or PVC conduit with insulated wire rate for wet locations, or you can use cable rated for direct burial.

Where are you located?

Some choices will depend on the amp rating of the new feeder.

Thank you for the prompt response. Im located in Texas. I have another question... I want to run the wire over the a post or the building. What grade of wire should I use? Wire burial is out of the picture. Thank you.

Aerial rated cable, often called Triplex, you may need 4 conductors, called Quadriplex.

Next need to determine the size conductors.