Francis, I would like to suggest that you check out the new AmDeck floor & roof system by Amvic.
It is probably the best fit for your intended application- while being both user friendly & affordable.
Click on
http://amvicsystem.com/amdeckfloorandroofsystem.aspx then navigate all the options...
Then if you would like to verify the loading numbers, call toll free & speak with the in house P.Eng.
named Amr-whom I'm sure will be glad to discuss these things with you.... Hope that helps.
Take care,
C. Kerr