I think you should start on learning your way around all commands (at least know a basic concept of what every command does) before starting to work on a map. Sincerely, if you don´t know how to make something as easy as this, then i suggest you to drop your project and start learning some map-making techniques, the most basic stuff is learning to do a decent building and learning easy tricks like TP, set your spawn on convenient spots, make a custom spawner or /summon if you want to introduce PvE fighting. Also learn how to make a good lobby, to avoid players from getting outside the map. To start learning how to build, watch some youtubers (false symmetry and grian are two geniuses on building). To start learning how to use command blocks, well... I use tools like these Some command generators and Heads for detailing just to give you some examples.