For the insurance company to begin a quote they need the estimated value of my 2 story 20x40.
How would I figure this amount? :-X
[size=56]make something up[/size]
If you want a better answer than that, then you get to do what the real estate agents do when they try to sell a house in a new area. See how other houses in the area are valued--do, or look at, "comps."
Or, you could ask the tax guys about what they're going to charge you and figure accordingly.
Amanda is right, comps is the way most assessors would do it.
Here is the link to my cost estimator which you could use to estimate "replacement value" which is the other way to get an insurance number.
http://www.countryplans.com/costs.html