Sorry, misunderstanding 
I do not mean the layout. I just want to know the general facts and how I have to prepare my document and the settings for the printing shop.
I know that A-size sheets are not square 
I want to trim it, yes. But I want to use one A4 page for two pages in my document, do you know what I mean? An A4 page is 297mm high. My brochure will be around 145mm (* 2 = 290mm + trim...). Is this possible to be printed on one A4 page borderless? And what do I have to do for the cover? Does it have to be bigger than the other pages?
This brochure will be printed over 100 times, so I want to save money and print it on A4, not A3...Hopefully my settings are correct?
Thank you again! 
