Can someone pls submit a tutorial?
Its actually really easy.
Open hammer and make 1 brush in the middle of the map area.
Save it.
Open file with notepad
scroll down until you find a section called 'world'
there will be one solid.
the sides defines a side of the brush
get some paper and start plotting each side until you know how to change it
try to change it
try and open in hammer. if its wrong it will say it cant load the brush.
fix it.
try again.
get that right, make a second brush in notepad....
repeat.
---
as for the comment about making a map in hammer...Yea, that would be fitting.
Not knowing what people are going to come up with, mine may appear like it was made in hammer vs. the couple screen shots people have posted. But, if people compare it to other maps I have made, i think it will show through that it really was notepad.