A "cost that contains " may be a spell's total cost, an activated ability's cost, a suspend cost, or a cost you're asked to pay as part of the resolution of a spell or ability (such as Broken Ambitions). A spell's total cost includes either its mana cost (printed in the upper right corner) or its alternative cost (such as suspend), as well as any additional costs (such as kicker). Basically, if it's something you can spend mana on, it's a cost. If that cost includes the mana symbol in it, you can spend mana generated by Rosheen on that cost.

e se ho in gioco [card]doubling cube[/card]? i 4 mana in pool diventano 8, gli altri 4 sono spendibili per tutto, o solo per magia con X?

12/1/2004: Any restrictions on the mana in your mana pool aren't copied. For example, if you have {W}{W}{B}{5} with no restrictions on it in your mana pool and {U}{U}{U} that can be used only to cast artifact spells, you'll end up with {W}{W}{W}{W}{B}{B}{10}, {U}{U}{U} that can be used only to cast artifact spells, and {U}{U}{U} that can be used for anything.