This one takes a tiny bit more pre-planning than a regular shelf. When you measure, you'll need to take into account your baseboards/skirting boards, where any light switches, fixtures or electrical sockets are located, as well as the location of any other architectural or decorative details (like pipes or skylights). You'll want to make sure you have plenty of space so that the Wardrobe (and its opening doors) don't bang, obstruct or cause clearance issues.
Next you'll use your measurements to design your Wardrobe in the configurator. Once again make sure that you have enough clearance for all doors and drawers to open freely, and not bump bedframes, celiling lights or other furniture. You'll also want to design your Wardrobe 10cm less than your actual ceiling height height to allow room to assemble it easily.
For more detailed instructions, the Measuring info pop-up in the online configurator will help guide you.