An absolute minimum size would be about 2' x 5 or 6'. Much larger would be better. You may find that you're going to have to seperate them. Generally a single female kept with a male rarely works out in the long term. Most Hermann's males (regardless of which subspecies) are very aggressive and pester females constantly.
^ Listen to this guy he's an expert.
But yea two need alot of space. I know that many times people will put two females per male so they can each get a rest from him. Also putting up obstacles and hides around the enclosure so they can be hidden from vision by the male is another good way to do it.