What is to the left of the green wall? Do you have things you are wanting to display there or just looking to fill an empty void? And what will the long room be used for?

How mant books need to be there ? I love books but not as decor and for sure not now in front of a feature wall.I do not find loaded bookshelves airy BTW. I need a lot more info so post that her ein comments DO NOT start another post . The space looks unfinished so IMO too early to decide decor for that wall unless you have a ton of books needing display .

If the rest of the room was fully finished/decorated to give us some style ideas but right now there is no reference to the rest of the room. I would suggest you put this bookcase money into the rest of your decor first THEN move onto the accent wall which will hold a TV? maybe?

Is that a radiator on the right adjacent wall? If so, it may limit how close you can put the edge of a book shelf. If your measuring tape on the floor is the planned size of shelving, then it is probably okay though. Will the book shelves be a stained wood? Or painted? I would also get rid of the green accent wall and paint that wall the same color as the other walls. If painted book shelves, then also paint those the same color as the walls. But if you really want color there, paint the back insides of the bookshelves only.

Only you know how it looks in person, but on my monitor, the green doesn't look like the right green to go with the floors. I think all the previous comments are on the money. Paint that wall the same color as the rest of the walls and furnish everything else before thinking about shelves unless they are more important to you than we know. Once you have the rest of the room furnished it will be more obvious what kind of shelving would be right. What you intend to put on the shelves matters too.

Sorry, didn’t read your post carefully enough. You are saying metal or stained wood shelves and metal? Then what did you mean by something smaller and “decorate the sides”? That’s what threw me off…. Did you mean something like a low cabinet or side table with art above and chairs on either side? Regardless, I think I would paint that wall the same color as the other walls. Hard to make suggestions without a better idea of your decor.

On the left it’s just a hallway. The bookcase or shelving unit will be used for both books and decoration. The wall is around 3 m wide and 2,8 tall . The wall is the one side of a living room . On the other end there are the sofa and the tv

Some options I can think are these. Any suggestions ?

I like the last one.

The success of a shelving unit will be based on the size fitting the scale of this room These are from Crate & Barrel and CB2 in heights from 78" to 96"

If all the furniture is at the other end of room, I’m not sure if any of those will give enough visual weight to balance the room.

Suggest waiting until your furniture is in place and be sure to complement its style.

If it were me, I’d add a long credenza, accessories and art to ground that space and reflect your personality.

Bear in mind that with any shelving unit, metal, wood, whatever, filling those shelves successfully can be a night mare. Ask me how I know. I landed up getting doors installed on what I thought would lovely open shelves.

I'm not a fan of open shelving. Too much work. Maybe a closed cabinet instead.

Thank you all it was really helpful . Yes the scale troubles me . I’ll wait for the new sofa before making a decision. Open shelving may be hard to decorate but it opens up the space. A closed cabinet would make the space feel smaller I’m afraid

A credenza is not a bad idea