Can some one explain map size and skyboxes to me?

So I have done a lot of research, I and my friend have learnt a lot from hammer, so be it, we have only had two days in it so far, so far I know how to apply textures (and sort of scale them), make and holo shapes, even started with doors and more advance stuff.

However, I have came accross and issue, currently we want to make a roleplay map, we’re starting small and not jumping straight to the big stuff or though we have lots of ideas, and now I have an issue, I made a skyscraper a player spawn etc, then out side of that placed a skybox camera thing, with skybox models arround it in a box, I then applied a sky texture how ever it made the skybox buildings invisable and also when you spawned the sky was a void with glitchy messy stuff, the menus even ghosted over it. I don’t have screen shots, but it being so early I think you can make a good enough image in your head :p, sow how do I fix that.

Also how big can a map be, I know people make it bigger then when they go out side the map boarders they get suspended in the air like a ufo is stealing them in some Independence Day style and all entity’s are removed, so can some one compare the map scale to something I can imagine so I have an idea of what I’m working with, thank Ye.

Let me answer your map size question:

As far as I know, the maximum map size is a little bit smaller than the hammer grid itself, the thing about the Source engine is that it doesn’t handle large open areas very well. It was designed for room-to-corridor, corridor-to-room kind of maps. Now granted you can create a large open map; but it will take a significant amount of optimizing and planning. This cannot be stressed enough

If you pay attention to the two most popular roleplay maps (the original evocity and original downtown). You’ll find that they are sectioned off into different areas. This is how you get away with making large maps (even though the original downtown isn’t necessarily big).

Now, how do we optimize? There are several tools(specifically, entities and techniques) at your disposal to achieve this. I highly suggest you read on about visibility optimization here.

Read this and the 2D and 3D skybox links, it should explain most of your questions. Despite being heavily outdated and questionably correct in some content, the VDC is still a very good resource for new mappers.