To make a game builder that broad would be slightly unreasonable, since it would take so much effort to learn, which could be time taken learning SmileBASIC itself
Now, are you wanting a platform game builder, RPG game builder, something specific?
The key for a mario-style level building game is [1EKEDV3E] you should take a look at that one while you're at it
1そうだね プレイ済み