The second choice is to visit the house and make your own drawings.
Good luck and may God bless
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.
If you have an Iphone or Ipad, you can use the "MagicPlan" app. Allows you to take pictures of rooms and develope your own floorplan. Free to $5. I haven't tried it yet, but there are a lot of good comments at the App Store.
Most homeowners misplace their floorplans. And most are NOT blue prints but marketing materials from the builder. Most Realtors will help you draw on paper a rough sketch, but other than the app your left only with photos and possibly virtual tours.
If you need a realtor, I'd be glad to help.