Run of House, or ROH, generally means you will be staying in a room decided upon by the hotel. In it's simplest form, ROH means you will get whatever room is available at the time you check-in.
If the hotel has a deluxe room or a suite available, you "could" get a nicer room than you would have if you had requested a specific type of accommodation, but you could be booked into a lesser valued room. It all depends on the hotel and how the hotel handles Run of House.
Sometimes, a hotel will have a specific type of room which is their standard Run of House room, which will be booked to those that do not request a specific room type.
If you want a specific room, view, or location, go ahead and choose it unless you are choosing the most basic room the hotel offers, then you might be better off to choose ROH, and hope for something a step or more better than the basic room.