How to make an inverted object?

[ivla]

Have to make a cover in STL for a button. So i designed the button, nothing fancy. The goal is a cover as a mould over the button.
Bigger box over it, but BOLEAN > 'difference' doesn't work. Wat is the best way to make an object inverted / as a mould?

Maybe, "shell extrude" helps?
Select faces as you need and use it - you will get a separate object.
If you need some space (a gap) between objects - use "shell extrude" twice, one by the distance of the gap and another to get "cover" object. "The gap object" should be deleted after.

Something like this:  (orange is the selection color)



Select faces:


RMB:


Use direction "by normal" - you get a "gap object".


After extrusion leave faces selected and repeat "shell extrude" by normal once more:


View with deleted "gap oblect":


View from below to "cover" object: