If you want an aquarium in shape of a cube with volume of 8000, then use the formula for volume of cube to find the length of one side: 
V = s^3 
where 
s = side length 
Substitute, 
8000 = s^3 
s = cuberoot(8000) 
s = 20 inches 
Well, if you have to draw this on a graphing paper, you should first make a scale to fit the drawing, like 1 inch = 0.5 cm, so a side length of 20 inches is equivalent to 10 cm on your graphing paper. 
Hope this helped!