Provide an Est. overall Monthly views of your website, or overall downloads of your app.
Give a descriptive name to your space, e.g. "Top of Website 728x90"
How many Advertisers can advertise here at once? (Different advertisers can be rotated within the same ad space).
How many ads should be visible at the same time? (different ads from different customers can be visible side-by-side, this can be useful for 125x125 square button ads, or link ads.)