Condo Railing Bar Project

I am looking for help to produce a design for a prototype railing bar top. The design need to be simple, aesthetically pleasing and work with any size or shaped patio railing. The railing bar tops are intended for condo/urban homes, small patio spaces. I have include sample photos of custom designs I have seen online. I have also included pictures of a sample hanging railing bar that I made for my own apartment. The bar needs to be designed so that it can be easily assembled and can be shipped flat. With the sample bars the material was wood - however I am also looking at substitute materials that would weather better then wood and more durable. The biggest design challenge will be the attachment system which will securely hold a bar top to any sized railing, both flat and round and make it level. The bar top design could either hang from the railing or sit on top of the railing. I am open to suggestions on the final design and dimension for the bar but in the same that I made the dimensions were: 48" wide x 11" deep x 6" high.