Please create a rendering for the approved tag man_made=bunker_silo (Wiki documentation). For those mapped as polygon I would propose a rendering as a grey area with a highlighted (dark grey) frame.
Now there are several hundreds mapped, but I would approximate that the number will increase to several tens of thousands.
See also https://trac.openstreetmap.org/ticket/5098 .
These are common in rural Bavaria, in farm yards and also just at some field's edge. I would like to see these with a similar colour to farmyard, a bit darker.
http://taginfo.openstreetmap.org/tags/man_made=bunker_silo - 1243 objects mapped
I see no good way to render these objects without making it highly confusing.
Also, such objects are not highly important, I think that rendering them is not the best idea.
I like the rendering-style proposed by daganzdaanda: "with a similar colour to farmyard, a bit darker".
There should be a rendering because in the areas covered with a bunker_silo is nothing else.