Might be an unpopular opinion but it's 2018 and you can easily find front-end developers with enough design sensibility and UX common sense to not need designers at all for building an app. I've been doing this for 10 years, in different companies, with different people, and I've seen many front-end developers being very successful at designing apps on their own.<p>I personally enjoy it too. I usually draw wireframes on a piece of paper and iterate, if necessary, with the product team and/or the users. Then I directly implement the wireframes in React or whatever technology the company uses. Some developers like to use Photoshop or Sketch, but from my experience, a digital mockup doesn't add much value over a drawn wireframe so I just skip these tools.<p>-<p>PS: Building a company's website is different than building a company's app. Your CEO/marketing team will want logos & branding colors (reusable by the sales & marketing teams for their presentations), illustrations, videos, animated menus, complex layouts, fancy gradients, parallax scrollings (ew!) and so on. A designer will probably be better at this job (and more interested in) than a developer.