[RELEASE] Aldéz's Portal Prefabs
When you have no previous mapping experience, your first stop would be Valve's developer site. Just start with the "getting started" section and work your way through the articles. Once you've got a hang of the basics, you can move on to the Portal-specific part of the site.
When mapping for Portal (or any other source game), there are many non-obvious but critical things you need to know about, like preventing map leaks, entity scripting, lighting techniques and optimisation. All of those things are explained at that website.
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reepblue wrote:
If you want a challenge try mapping for Left 4 Dead. Then we can talk about hard mapping. .
I haven't mapped for l4d yet because the sdk isn't out and I can't be stuffed to set up hammer, but reading valve's tutorials it looks easier.