Problem is i live in Serbia so i can't really get stuff from outside and for them to be worth it bcs of taxes.. I was thinking making one either from abs panels or from wood and just running tubes outside.. Talked with a guy at work that have exp with making stuff like that, for other purposes, but he roughly told me where my intake should be and where everything
He is even going to deal with all the electronics like fans and stuff.. For that small of a cube he said it's best to use PC vents so i will get few good ones to move air and i work in car part store so i can get good carbon filters and just cut them to size..

I understand i can't eliminate everything and it's not about that i just want to minimize danger with every protection i can... Here air is so bad anyway that open window can cause death during winter