There can be intellectual property rights involved, but I would guess that most basic floor plans have been tried many times, so, unless the floor plan you like has something rare or highly innovative, you may not have a problem. As mentioned, this is a question for an attorney.
In terms of obtaining a basic floor plan, sometimes the most direct approach is best. The first thing I would do is talk to the owners of the home and ask them. Unless they feel that the floor plan is unique or highly personal, they will probably be flattered you like their home so much.
Front Range Real Estate, Ltd.
Prudential Real Estate of the Rockies
Best of luck!
There may be some 'intellectual property issues' if you try to copy an existing floor plan exactly or pretty closely. That would be a good question to run by a lawyer for sure.
I am currently in the process of building a home myself and decided after looking at 100's of homes as a realtor - and 100's more online - to meet with a draftsman and have her custom draw up a set of plans that takes what I liked in a large number of homes and combines them into my own dream home. She has been amazing and has also brought to the table many other good ideas that I had not thought of.
Her business name is Donna Bagdy Drafting and Design, Inc. email: firstname.lastname@example.org
She also has had good ideas to help us keep the home within budget.
Hope this is helpful and congratulations on your home building project!