UH - thanx guys - these are a lot of options - sorry for asking noob questions.
I will try and hopefully one of these options will do the job.

have a great day and thanx for the support

Dear Community,

my plan is to create items in SketchUp which i want to product from modelling concrete. In order to do that i need the "negative" of this item and send it to a 3D printer.

i.e. i want to make a cylinder -> i need to get a cube with a cylindric hole inside - clear i guess.

My question - is there an easy way to generate NEGATIVES or INVERT my objects in Sketchup? becuase some of the items simply get too muss to translate them in my head into the respective negative form.

Maybe someone can help me with a hint or a plugin?

Cheers guys
hans