Legaly, if you adapt or create derivative works from copyrighted material, you have violated intelectual property rights and could be sued. It would be a breach of contract to sell something derived from a website if the terms of use of the website were that the materials were for personal use only, and you could be sued on that basis, too. If you do come up with it fully independently, you should be ok, but uf sued, if therr is evidence or documentation that you visited a website, that would be evidence that you did take, modify, etc.another's design.