Faciō, "to make" or "to do", is a common Latin verb. It's famous for being suppletive: it's missing most of its passive forms, and instead uses the active forms of the separate verb fiō "to become". (Compare English "go", which lost its past tense and had to steal some forms from the separate verb "wend".)
If I wanted to say that something "must be made", using a gerundive of obligation, how would I do that? Is that one of the rare passive forms of faciō that does exist, and can be used normally? Or would I use a gerundive of fiō instead, even though it's morphologically a passive form?