Question 164842
If you were just trying to make a cube, then the cheapest numbers would be W=600 L=1 and H=1
However this is not possible because you are trying to construct a steel building.  
You need to identify what the limits are that you can live with for the height and length and then make the rest of the measurment the width.  
A 1 meter tall building might be cheap but it would also be worthless.

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