Agriculture property deemed unbuildable?

[Gary Laws]

How do I find out what makes a property truly "unbuildable", and what steps would be needed to change it? I am new to this and am asking where to start and be well informed before buying it?

My plan would be to have a foundation poured for a manufactured home on a triangle shaped vacant land on 1.5 acres adjacent to a city paved country road. The property has access to power, and likely needs a well and septic. Could it be because those two items are not yet available that deems it unbuildable?

The property is in Washington State and is classified on the country records as a code A-10 and agricultural. It is not wetland designated, fyi.