I built one last year and made it 36"X 36". I wanted it strong so I constructed it using 2X6 to make the square of the landing. On the inside of the landing frame I nailed 2X4s and then cut 2X4s to fit flush inside the frame to provide the deck for the landing.
I used 4X4s for the legs cut to length so the landing is even with the floor of our 5th wheel when it is level. Those were bolted to the inside of the landing frame at each corner.
I then made the stairs using 2X8 sides with 2X10 treads mounted on these: http://www.strongtie.com/products/connectors/L-LS-GA.asp#gallery
Sorry I don't have plans or photos.
All I can provide is the basic components used and hopefully you'll be able to picture what I did.
