At first, you have to understand your concept of building a website. After that, you have to note down the functionalities of your conceptual website. In documentation, you have to write all features for your web project. Then find some web designers and take interviews by describing your website concept and overall functionalities of your website. After that ask the web designer to note down your concept in his/her words. Try to ask some questions about the documentation. If the web designer satisfies you just hire the web designer.
Now days hiring a web designer is the toughest way to choose. Because there are now several marketplace from where you can hire web designer among millions. But if you go there post a project you will be amazed by receiving the proposal from many web designers. You will see the huge price difference between the proposed price and your expectation. You will definitely lowest price with the quality response. In the end, you lose your patience, time and money too. Professionalism does not reflect only in the way of communication. If the designer shows eagerness to understand the project first and after asking for negotiation so you can take a risk to try the web designer. You have checked the previous portfolio work also and understand the credibility of their web design and development process.