New to modelling

I’ve recently started learning how to model using 3DS Max. I just have a couple of questions though.

I’ve watched some tutorials on the basics of 3ds Max and I’m just wondering how I would find out the size of a model I make on GMOD. Also, is there any specific things required to model besides 3ds Max?

I find size through hlmv’s physics tab (hitbox size)
and you need source SDK to compile models you make.