Except for recently, it's been a while since I have mapped. But the usual 16 units seems a lot bigger than normal, maybe it's been too long? Anyways, I've looked but I didn't find any information on this, what sizes should I make these:

1) Windows that you can crouch through.

2) Doors

3) How thick a wall should be.

4) How tall, thick, and wide is Gordon?

5) The height for a single floor of a multiple floor building.

I know I'm asking quite a bit here, but it seems as though the sizes have changed since HL1, and all I remember was that Gordon used to be 32 wide or tall when crouched.

if you want exact figures, its as simple as a small test map away, but at a guess id say:

1) 45 units
2) 90 units
3) 32 units
4) inside height 128 units

as its not an exact science, i feel these numbers are close, but as i said, its as far away as a simple test map.