The IKEA closets have been a bit of a challenge on both ends - from the purchase process to getting the correct rough openings. In the end, it’s probably still worth it, as the doors on these things are still superior to what we could get for the price point with a totally custom closet system.
Things to keep in mind: How the baseboard will interface with the base of the wardrobe system, how to treat the last bit of space used for “rough opening”, and pull options. To my knowledge, the system completely forgoes any sort of finger pulls, so we need to install additional hardware for ease of operation.