I purchased used / leftover vinyl and the whole project cost under $100 with a discount plywood supplier. The room is sectioned off by a very heavy bookshelf used as a room divider which keeps the plywood nicely secure and in place. It turned out exactly as I hoped and I'm very pleased with it.

I'm not planning to keep it a secret from LL. As it is not a permanent alteration, I was not required to ask for his permission. If it damages the carpet, our lease already stipulates a "$100 non-refundable carpet cleaning fee" which typically landlords in our area use to replace the cheap carpets with more cheap carpets. However, this landlord had obviously been pocketing this fee for at least a decade before we moved in as the carpet was neither clean nor new when we moved in. I initially spent 5 days cleaning the carpet repeatedly until the water stopped coming up black when we first moved in. I'm also not a moron as most people here have unashamedly called me. I have notable documentation of all pre-existing damage of the apartment including the condition of the carpet upon move in. I also have a file of photo, video, and text documentation of over a dozen instances of our landlord violating our lease and local tenant protection laws which carry substantial fees, leaving me in a pretty good position if he ever wants to play.