The dimensions are on the photos on the Ikea website and gives an idea of height. Teen wise my sons are just shy of 6ft so we have no baseboards in case they want to hang their feet off the end of the bed.
Ikea do a range of storage beds, like Hemnes, Brimnes and Malm plus others. Just search beds with storage in the Ikea search bar.
Unless it is a surprise I would take the teen with you, make a day of it, eat in the restaurant. Be aware some of them open at least 30 minutes early for browsing and the restaurant is open too meaning you can get a hearty breakfast and then go check out the beds. You can browse the store until the kitchen items section (pans, crockery etc) that part is usually roped off until the actual opening time.
I just live near an Ikea.