I have two turtle ~4-6 months old. If they are female and grow as expected they can be 1.4kg each. 

I have designed a basking area, which can hold 4kg and can swim on the water surface. Something in my opinion very important to save place in the aquarium / terrarium.  There are holes to attach the hole thing to the aquarium walls. Use a aquarium silicone to glue all the parts. 

Of course now the turtles  are young and lightweight, I have made a hole in the cover of the basking area and I can put water in it, to make the area go deeper in the water, to stay stable. I have used this standard fitting to close the hole in the cover.

Enjoy ;)