Generally, you can be sued for infringement whenever you make, use, etc., anything that comes within the scope of any issued, unexpired, not-yet-invalidated claim.

There's a nebulous experimental-use exception to liability; it's currently of uncertain scope [0].

> If I build a factory that produces chairs, and then hoard all those chairs in my house, can I be told to knock it off?

Generally, yes — if the chairs come within the scope of an issued, unexpired claim that hasn't yet been invalidated, then simply making the chairs constitutes infringement of that claim.

> What if I build the factory and then have it just stand there, producing nothing?

If the factory itself doesn't infringe a claim, then there's no infringement under the stated circumstances.

Same disclaimer as above.

[0] See, e.g. https://www.lrrc.com/webfiles/TCL-KK_DS.pdf (not an endorsement).