The increasing demand for immersive digital shopping experiences has driven retailers to explore virtual showrooms as an extension of their physical showrooms. IKEA, a global leader in furniture retail, has embraced digital innovation by venturing into virtual showrooms. However, the lack of established Principles for designing user interfaces (UIs) that ensure usability specifically in virtual environments presents a significant challenge. This study addresses this gap by developing a virtual showroom prototype for IKEA and evaluating its UI elements based on established usability design principles. This work has two-fold contribution, the first was the prototype implemented according to IKEA’s user experience (UX) requirements as well as UI elements evaluated from the pilot-study. The second is the evaluation of the prototype, according to UI design principles, with prospective IKEA customers using think-aloud and cognitive walkthrough. The evaluation shows that the implemented UI elements contributed positively to the virtual showroom's usability, as participants successfully completed all tasks with a high degree of success. Based on the results, we discuss eleven UI design principles for implementing UI elements in a virtual showroom. These principles offer actionable guidance for future implementations to enhance user engagement, navigation, and more efficient interactions within virtual showrooms.