How to change the page width in omega 3?

@Hamid.D
I have 960px by default and I'd like to understand where did you manage to set it up to 1200px by default. Could you please share this with me?

Is there any common way to define the site width with some a value other from 960px?

The out of the box width for the Wide layout is 1200px, for the Normal layout 960px and for the Narrow layout 720px.

There is no UI option to change this, it would take manually changing the alpha-CSS files.

Thanks. As I understand that's the way it is. BTW. Have you tried the solution from this issue?
#1124820: How do I change page width to 970px?

That solution was for 7.x-2.x, Omega 7.x-3.x uses a different setup regarding the naming of the files. All grids are set in the alpha theme, 960.css isn't used anymore. There might be a cookie cutter way to do it though. :)

As there is no solution offered resetting to active.

Actually I have done exactly what I wrote above for 3.0-beta3.
Try the foolowing
* Go to the site above
* Insert desired values
* Paste generated css to sites\all\themes\omega\alpha\css\grid\alpha_default\wide\alpha-default-wide-12.css
* Replace all '_' with '-'

Try reviewing this, please :)

If it works for you, and you get the desired effect then it's ok isn't it?

PS: why do you use the beta 3 version?

I was lazy to update :)

It is not possible to review this because it is not clear what should be reviewed. What site are you talking about? What are the desired values?

This is exactly what I did. I determined this separate from reading this. But I also found that at the bottom on the css files that the 960.gs site generates has some clearfix css. This stuff already exists in the omega css. So you need to remove it from this new css file, otherwise it creates issues.

To resize 1200 to 960 I went to http://grids.heroku.com/ and set my specs, downloaded the css file and then updated the appropriate css code (in my case omega/alpha/css/grid/alpha_default/narrow/alpha-default-narrow-12.css

As noted, remove the clearfix stuff at the end of the heroku css, as indicated by pthurmond.

and I really don't like this solution. I will lose these at the next omega update (unless I "park" that css file appropriately)

Update:

There is a way to change the grid size, by adding your own grid with your own specifications. The documentation could be tighter; right now my custom grid works except for the grid.png file isn't displaying, and several others are having issues with this on that page.