Mine is very, very simple.
http://img.villagephotos.com/p/2004-...0/P8120031.JPG
http://img.villagephotos.com/p/2004-...0/P8140032.JPG
http://img.villagephotos.com/p/2004-...0/P5170053.JPG
I used 2x6 for the joists, but wish I would have used at least 2X8's. I put each 1 foot on center and 3/4" OSB and it is plenty solid. To add a touch more height, I laid a 2X10 flat on top of the riser and mounted th seats to that. The OSB sticks out about .5" so I could mount rope lighting.
http://img.villagephotos.com/p/2004-...0/P8120031.JPG
http://img.villagephotos.com/p/2004-...0/P8140032.JPG
http://img.villagephotos.com/p/2004-...0/P5170053.JPG
I used 2x6 for the joists, but wish I would have used at least 2X8's. I put each 1 foot on center and 3/4" OSB and it is plenty solid. To add a touch more height, I laid a 2X10 flat on top of the riser and mounted th seats to that. The OSB sticks out about .5" so I could mount rope lighting.