Thanks!
My paper chioce was the problem -it's too thick -but a lighter one (170g>
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will be very vulnerable for tuching, transporting, etc! I need a lot of these, so I have around 80, but just from paper, without any plastic inside to make them more durable -it was much faster to buld them, but the result is like this.
For 6mm try GHQ paper buildings (this ones) they are very good quality ones -and free
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They're nice if you need some dutch or west german towns, villages, farms from the 1930-1970's.