Professional? There's no school or education to become 'professional'
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Level design is an actual profession for games, however it's the sort of thing usually divided(at least for larger teams). A layout designer will design the layout of a level in the most barebones structure, ending up with a blueprint of sorts detailing the purpose of the level, the flow, interactions and so on. Then a level artist will go through and design the actual aesthetics of the level around the blueprints laid out from the designer.