i've built 2 coops so far and Robin hasn't given me any option to build other farm buildings :< do i have to build a 3rd coop to get new options or smthn?
You may not have noticed the arrows at the bottom? Click on those to get to other building options. You can build them in any order - actually I'd recommend getting a silo before a coop or barn, so that you can get hay from cutting grass.
EDIT: here's a screenshot, click on the arrows circled in red to see other building options
On which platform do you play (with/without mods). Usually none of the standard buildings by Robin is blocked, e.g. coop, barn, silo. And you can build any of them in any order and as many you have materials and place on your farm. Maybe did you miss the right/left button to scroll through the options?