How do you make a WS map?

[Maestro]

I've become interested in mapping lately, and I was wondering how to make a map that works with Winter Survival. I was thinking of making an old, abandoned ranch that's hiding a secret underground research facility. If you know how to make a WS map, or have any ideas for the map I'm making, please comment. Thanks in advance.

[Sabb]

As far as I know, you only have to use the HL2 rocks, trees, and antlion mound models and they autoatically work (not certain about this though).
For making the items drop, I believe that requires a custom entity or w/e. I'm not quite sure how to do that yet, though. Just search around a bit on Google, shouldn't be hard to find.

[The punisher]

Just decompile a WS map and then see what entities the mapper used. If its a custom entity, then copy and paste the name in google or copy and paste the entity to your map.