the person who published the plans would presumably stated any restrictions they’d placed on their use. The point of publishing plans is so people will make things from them, so they’d need to place pretty clear restrictions with them if they weren’t offering an unrestricted license on things people would make
What you’d need know though whether the person who published the plans holds the rights for the design themselves (or to all the aspects of the design). If they’ve unwittingly or otherwise included details which someone else holds rights or patents to then making something from those plans on a DIY basis is one thing, but taking it to market is something else. Generally though published plans tend to be just variations on traditional designs and constructions.