Are there any CSG tools for Unity where I could build basic levels? Is there any free tool that does this that is meant for level design specifically and not a general modeling tool as I’m not a modeler and I often hard a hard time learning modeling tools ie. please don’t say Blender.
I’m looking for something like Valves Hammer or 3D World Studio but need a way to somehow get those files loaded into Unity. Anyone have any ideas around this?
You mean Booleans? But you WILL need to learn a modeling tool. Yes, it is hard, things are hard, making games is hard, live is hard. If it wasn’t hard, people wouldn’t be earning money with it.
Get Blender, use the extrude tool a lot and you can make almost every basic shape using it.
No, Unity does not include a CSG tool by default, like Unreal for example. You will need to gray box your level designs in a DCC app, like Maya, 3dsMax, etc. and import that into Unity via FBX. If you’re having this much trouble figuring out how to get started gray boxing your Unity levels, it’s only going to get much worse for you going further into your development cycle.
Have you tried using Unity primitives to pre-viz level geometry? It’s not very advanced and definitely not robust, but I’m sure you could get some use out of it. Good luck.
could be an idea to let us know what you’re actually needing CSG for? it’s an old approach which is very limiting when you want any form of detail or uniqueness in your art by todays standards anyway
if it’s just greyboxing, use the Unity primitives! If it’s for the actual detailing… why?
He mentions basic levels, so he prob wants/needs only limited features that will help him/her iterate level designs quickly. We use Unreal at work and our designers use BSP to quickly test level layouts and try out design ideas. Once they are happy and get approval from their leads, they come to us on the environment team and consult with us on what they want, and then we make the magic happen 
This is prob what the thread starter wants, or something along these lines.