We are lucky enough to have had twins twice.  We have two girls and two boys.  It is unusual, but it is never dull.  When they were old enough to have beds, we opted to buy them Bunk Beds so we could save them some room to play in their rooms.  This has been a great idea and has worked out for the best all the way around for us all.  The only problem we have is with the boys arguing over who sleeps in the top!  The girls have worked out a system week to week to share the top and bottom bunks.