"We roast some potatoes."
Translation:Arrostiamo qualche patata.
We = Noi
we roast = arrostiamo
some = qualche / alcuni / dei
potatoes = patate
There are several ways to translate "some" and the invariable qualche (qual+che) is the most commonly used, - but it requires the following noun to be in singular, i.e. qualche patata.
"Arrostiamo qualche patata."
Or we can use alcuni, - but then we have to mach the gender, i.e. alcune patate.
Arrostiamo alcune patate.
Finally we can use "di + article" to express the indefinite quantity, i.e. delle patate.
Arrostiamo delle patate.
If Some Potato was the intended, then qualche patata would make sense. Delle patate maybe woud be a better choice, e vero? Qualche patata just seems wrong, even if qualche is to always to be followed by the singular. We're still tslking about a plurality of potatoes. I don't mean to seem argumentative, it just confused me...
If you check out gailemow's thread at the top of the discussion page, you'll see some discourse about that very question. In summary: if you're using "qualche", it is ALWAYS followed by a singular noun. Also, Marninger's comment give a good quick breakdown of a few different ways you could say this.