Normally a furnace like that has a cold air return on the top. What is missing is the plenum. BUT, if you only have one cold air return in the house and it is in the door, then that is the way it will be. Actually when the plenum is on the top, it's kind of a pain to change the filters. At least this way it is simple.
If it is the house you want and the inspection goes well with the Home Inspector, negotiate a second opinion out of the current owner for a full furnace inspection.