Designing Portal levels is harder than playing them through

I got Portal 2 and Rocket League along purchasing the Steam controller. The Rocket League only runs on Windows and I've played the single player of portal at a friend. I tried some community-created levels and made one of my own:

My portal level

I can probably play through any Portal -level that is playable, but it is incredibly difficult to design a map that is worth playing through. Even after checking through several great examples, I feel I'm not up to the task.