This is what our Ikea bookshelves looked like before the transformation. I have no idea what they are called but we got them a few years ago.
I began by flipping the bookshelf on its side and coating it with some primer. I also added 3 sets of casters to the bottom. I started with just 2 sets of casters but because it's so long I added an additional set in the middle.
I painted the top of the bookcase green and then added some blue lakes and some road decals that I got at Target.
Here you can see it in the playroom. We mounted the other bookcase above train/car table for additional storage. The blue fabric bins were bought at Target and fit perfectly. You can see the Ikea hack for Hot Wheels track holder here.