Most builders have floor plans on their websites.
If it is a pre-existing home, your Realtor may be able to pull a basic sketch off of their Stewart Title HCAD link that they have access to thru their HAR.com membership. Some Listing/Seller's agents may attach the origanal floorplan and/or Survey to the listing on the Agent side on the MLS
Do check out mine and my collegues websites to find you the Buyer's Agent that you feel comfortable with. Remember that the Seller's Agent has to put their Seller's advantage over yours first, so it is best to have a Realtor acting as your Buyer's Agent in your corner.