Hello !
So this is my first tutorial, its really, really basic, but I think creating skyboxes is one of the primary things you need to know before you start the mapping.
Situation # 1: the boxed room
So, my first situation where we will create a skybox. This a map set-up that most newbies should recognize: the boxed room. You've just learned how to create rooms, handle light entities and basic clipping of objects ... and now it's time for the skyboxes.
This is a picture our setup (the computer workspace in the middle is just to make it "feel" a little more like a room, and to make sure you know what's up and what's down). Make sure you have the default HL wads loaded.
Now, we want to get rid of the ceiling and look into the sky.
Your ceiling should have a light-blue colour now. Compile your map.
It should look like this:
Remember, for windows (with or without glass), ceiling holes and other more complicated stuff, you can use the same method. Just make sure everything fits exactly. (to prevent leaks and/or ugly skyboxes)
Situation #2: outside environments
To keep it simple, we will continue with the setup we had after situation #1.
The only thing we have to change are the wall-textures.
Select them. (not the floor.)
Use the same method as described in situation 2 to replace the textures with "sky" textures.
It should look like this now:
Compile your map. Who doesn't like some fresh air when programming ?
Remember, when you're creating realistic outside environments, you should mark the edge of your map with fences, or even better: with solid stuff like rocks or walls or trees ... this is also to prevent people from looking down to the skybox ... (you can also clip it at the place where people should'nt look over the edge of your map.)
(many thanks to Leperous, Fraggard, Jinx and Tracer bullet, the friendly dudes who explained me how to do this.)
So this is my first tutorial, its really, really basic, but I think creating skyboxes is one of the primary things you need to know before you start the mapping.
Situation # 1: the boxed room
So, my first situation where we will create a skybox. This a map set-up that most newbies should recognize: the boxed room. You've just learned how to create rooms, handle light entities and basic clipping of objects ... and now it's time for the skyboxes.
This is a picture our setup (the computer workspace in the middle is just to make it "feel" a little more like a room, and to make sure you know what's up and what's down). Make sure you have the default HL wads loaded.

Now, we want to get rid of the ceiling and look into the sky.
- Select your ceiling (by clicking on it in the camera view or selecting it on 1 of the grids).
- Hit the "replace textures"-button
- A window will pop up. You'll have to select your current ceiling texture in the "Find" box ... you can easily find this by hitting the browse button and select it from the list. (make sure "only used textures" is checked.)
- In the "Replace" box, you'll have to select the sky-texture. (In this guide, we will use the default HL skybox (desert), but remember that this can be customized at any time). Hit the browse button, and filter the textures by using the word "sky". Double click on one of the tiny squares and hit "OK" in the Replace-textures window.
You can change Skyboxes by going to Map > Map properites > CL_Skyname
Find a complete Halflife sky list
here: http://www.vlatitude.com/resources/hl_sky.php.

Your ceiling should have a light-blue colour now. Compile your map.
It should look like this:

Remember, for windows (with or without glass), ceiling holes and other more complicated stuff, you can use the same method. Just make sure everything fits exactly. (to prevent leaks and/or ugly skyboxes)
Situation #2: outside environments
To keep it simple, we will continue with the setup we had after situation #1.
The only thing we have to change are the wall-textures.
Select them. (not the floor.)

Use the same method as described in situation 2 to replace the textures with "sky" textures.
It should look like this now:

Compile your map. Who doesn't like some fresh air when programming ?

Remember, when you're creating realistic outside environments, you should mark the edge of your map with fences, or even better: with solid stuff like rocks or walls or trees ... this is also to prevent people from looking down to the skybox ... (you can also clip it at the place where people should'nt look over the edge of your map.)
(many thanks to Leperous, Fraggard, Jinx and Tracer bullet, the friendly dudes who explained me how to do this.)