looking for the floor plans of a house that i want to purchase?

If the seller doesn't have them, you will probably have to create them yourself. The other option is to (if it was a recent build) go to the city building department archive and see if the construction plans are there. Most people are hesitant to hand out floor plans as it opens up a potential lawsuit.
If this is a new house, go to the office of the building inspector for the city where the house is located. They should have the plans on file and available.
Go to the County Tax office and ask for the tax card. It will have a floor plan. May cost as much as $1.00. Some small towns around here (NH) cahrge as low as $0.25
If what you want is the architect's blue prints, keep in mind that they are copyrighted. You may have to buy them from the builder.