Building a wall in a rental property

I'd seriously consider a Byōbu, more commonly known as a "Japanese folding screen wall". Something like this:

^{The first decent example picture I found happened to be from etsy}

You don't have to purchase one (finding one for your 9-foot ceilings may be difficult). However the "folding" aspect - i.e. the zig-zag footprint will allow it to stand on its own.

You can cover the "panels" with drywall, fabric, paneling, or whatever suits your mood. The advantage is that you don't have to attach it to the floor or ceiling and, therefore, won't cause damage to the rental that will need to be repaired before you move out or risk losing your damage deposit.

Since you're willing to spend the money on lumber & drywall and dispose of it when you move out, there won't be any significant additional "disposable" cost in building the wall this way instead.

Look in your lease to see if an aquarium is allowed. This could make a beautiful room divider!!! A relaxing scene, a conversation piece and a bit of nature. To see what people are putting in their tanks, search for "aquascaping".

Freshwater or saltwater, there are tons of options Same for the cabinets. A good place to get started is Aquarium Co-op videos in you tube. Or your local fish store can set one up for you and even do the maintenance.

Have you considered some kind of feature hanging from the ceiling?

Give that this is a rental property, something like floor to ceiling drapes might be a more temporary solution to divide the room and only require minimal repairs when you leave the property.

You can also get specific "panels" designed to be hung from the ceiling to provide a visual barrier in rooms if fabric isn't your style.

Wait... buying a shelving unit is a nuisance. You buy it, then when you move out you sell it used...

Opposed to spending hours building a "wall", huge mess, materials, and so on... great chance of damaging apartment... then you have to demo it before you leave and throw it away - all needing to be done without damaging existing area. Building something that is stable without damaging existing area is possible but nearly impossible to be done and look good.

Just google/craigslist "office dividers". In almost all areas these are being given away - also if you have a "restore" (used building supply store) they have these too. Your best bet is find something on craigslist and then resell it or give it away once you move.

The problem with building anything is that it would need to be EXTREMELY bottom heavy to be stable and not drill into ceiling or walls.

If the objective is purely visual separation, a fabric barrier would work. One approach would be to use the spring loaded poles used to create temporary plastic film walls as dust barriers in construction areas.

White linen, muslin or similar could either achieve a bit of Japanese aesthetic. A bedsheet of the right pattern might look ok, and the poles could slide into the hemmed ends.

Zipwall is one brand, pictured here.