Scripting a Player Character Collider

Im trying to create a game with a Xenogears style movement and camera system. I created my own scripts for the character movement and for the camera and they are working as intended. I am now trying to make a script that blocks character movement with objects in the world (such as the floor and buildings).

My questions is, how difficult would creating a script to do this from scratch be and how would I go about doing that. Also if it would be easier to use the provided scripts with the scripts I have created.

I am not an expert on coding with javascript, and I am learning as I go along, so the provided third person character controller script is difficult for me to follow, so Im having trouble figuring out how to change it to make it operate as my created scripts do. After searching the internet for tutorials on how to do it though, I am starting to think this might be my best option.

Any help would be greatly appreciated, thanks.