Lineweight exporting from Illustrator

Hello! I'm a bit new to using illustrator (making a site plan right now) and I'm having trouble exporting.

my lines are 0.25pt and when exporting to pdf they become so thick

it's not as bad when I export as png but then I lose the way the pattern looks/contrast

I'm not planning on printing it, so what should I do to export and be able to have the same view as I currently have in illustrator, I rally like the way it looks and don't really want to change the visual? (Enhance thin lines is already checked off!) 

p.s: exporting it to photoshop also doesn't help 

thank you in advance!