That is called and "Island Spread".
Go to the Pages panel, click the drop down menu on the upper right of the panel and DESELECT "Allow Document Pages to Shuffle"
Add a new page and click and drag the page icon to the left until you see a bracket "[" and the page will be attached to the 1st page.
Repeat until you have the # of pages you want.
Click the image above to see a larger version.
Simply perfect, thanks a lot for the Answer!
I would like to ask you something again. I have right now 10 A0 Pages in a row/spread, but seems that I can put anymore. It this that normal? can't I add more Pages on the same row?
10 is the maximum number of pages in a spread (a vertical arrangement like you've created).
Thanks for the clarification.