Most of packages available on ROS are for indoor systems or were developed indoors as part of a research. I suggest you give this a read first link. This should get you acquainted with the problems you can and will have.
Second issue is that you need an active sensor to tell you about obstacles, if the area you mentioned is empty then you don't need it, otherwise you need a lidar or you need to pre-map that area.
Now to actual question, you need localization ( link ) to tell you where you are at any moment, then you need a planner ( link ) that will use your localization data and plan your movement accordingly.
Of course there are tons of different packages available, but this should get you started on the right track. Hope this answers your question.
