What I want to do is, if you know making a room in unity you would just use 6 game objects, but I want to essentially create a room without having to make 6 game objects, since this would make the game run slow and would definitely hurt the game, so what I want to do is I want to create a room with only a cube, problem is, is that a cube doesn’t have an empty space inside so I cant just resize the cube and add the player inside the cube. How should I go about this?
make a room in blender, also a few gameobjects with only a collider and material have little to no performance impact
Like AbandonedCrypt said, Unity is not really a modelling software. If you want to create geometry you usually use a modelling tool like blender, 3dsmax, maya, C4D, … However there are ways to create more complex geometry inside Unity. Unity now has a package (which was originally developed outside Unity) called probuilder which allows mesh creation inside the Unity editor.
Besides using probuilder you can of course create any kind of mesh using scripting or your own tools. The Unity editor and engine is extremely flexible and allows to extend the stock tools with your own. Though creating your own tools can still be quite difficult depending on your experience. Though just like probuilder you can probably find tons of third party tools, some for free, some paid.