Half land, half water is way too much land! You need a lot more water than land, the basking spot should be big enough for them to move away from the heat source if they need to, but it needn't be huge.
A heater is only required for hatchlings and tropical species, temperate species don't need heated water after their first year.

Tomcat a 3 x 3 x 3 tank would be great, total volume would be approx 730 litres, I'm not sure where you'd get a tank that size though shrot of having it custom made?