Well you didn't give anyone anything to go off of. So I am not sure what they are going to help with.
You can check this page out for a better understand of 6th orders if that is all you're after. There are most links on the left side of the page with greater detail.
If you want someone to design you a box you should post all the details and then maybe someone will. I don't do 6th orders myself but maybe someone else will chime in IF you post all the details. By that I mean - Dimensions you have to work with, T/S parameters of the subs, Power you are working with, and what type of sound/goal/spl/response you are after.