it looks to clean & nice to be done in AE, but then again i could be wrong.
i would first make a gradient in illustrator, simply because they look SOOOOO much better than the ones in AE. Import the layer into AE and then duplicate it. Make both of the layers 3d, and then set them up for one to be your wall and the other your floor. heres the catch. the gradients need to go from a light to dark. not necessarily white to black, but I would use white & a color of your choice. Make the 3d layers so the white parts are touching. then add some AE lights, and start messing with the material properties of the wall/floor layers and all that stuff.
this is not a perfect explenation by any means, but if you’ve enough experience in AE, you’ll be able to figure it out. if not, just repost with some of the problems you’ve encountered and i’ll try to explain in better terms.