There are tons of ways to make a dock. A lot of people on the turtle forum like to make above tank basking areas. It gives the turtle more room out of the water and then you can fill the tank all the way up.
I bought my g/f one of these docks and her turtle really seems to like it. Zoomed turtle dock
Its really nothing more then a piece of hard foam on a rail so it can move up and down with the water.
Heres the link
to my photobucket album with the turtle projects I was working on. The ten gallon was setup so that I could take care of my g/f's res for a few days. The 30 gallon was never finished as it wasn't coming out the way I wanted. There was supposed to be a waterfall on the left and basking are on the right. The little rock outcroppings were going to have pots with various plants growing in them and moss stuck here and there. This is now my planted tank.