how to make a turtle island/raft??

i have a 1300 gallon pond and need to make a floating island for my
red ear slider that is about 2 years old and 7" wide, anyone have any
links ,diagrams or suggestionshow to make a floating island/raft that
will adjust to the water level?? my turtle must be half way blind?? i
made it a ledge on the side but it doesnt seem to be able to find it
or the water level has to be just right for the turtle to be able to
climb up on it. any suggestion would be great and my turtle will thank
you and a cheap solution would be good too!! water is warming up
and i know it wants to get out of the water to bask.