Is it permissible to build a website that enables web developers to showcase their previous work (websites that may be Islamically inappropriate), and allows visitors to request websites from them?

There is no impediment to building a website where experienced individuals can display the websites they have created, so that those seeking website creation services can connect with their developers and creators. This allows them to benefit from their services and compare them by reviewing their CVs and experience in this field, as these are generally permissible services.