Hello again

I was wandering about how larger projects are actually structured in the real world. I know of the use of UML diagrams but am curious as to how the design of large projects are done.

I know this is a really ambigious question.

My project which is really quite small is already having further structuring problems although I am trying to sort them ASAP.

I have a class called Collisions - this takes care of normalising,point to plane,bounding boxes and barycentric co-ordinates testing. This is linked directly to my enviroment class - this draws things to screen and checks for collisions between the player and the enviroment.

This is finally loaded in my main that passes the player co-ordinates and wall co-ordinates to it. My main then also interacts with my controller class and camera class.
Does this structure sound reasonable?

It seems to work pretty well so far I understand that in big projects things will tend to get buried such as Linked list or VectorMath classes etc.

Are there any good tips on designing how the code should run. Should you start with the main and figure out what needs to interact together? Or do you do as much work as possible only adding it into the main at the end?

Really interested in how the real world works and software engineering design approaches.

Many thanks