So IKEA sliding doors come in 2 height sizes, 201cm and 236cm and 150cm and 200cm widths. My concern when fitting was the height the fittings need to go to for my own design. I went for the 201cm high doors because of the restrictions in the high of the rooms I was fitting them in.
So the important measure I needed was 1925mm from the top of the bottom rail to the top of the top rail. See picture below.
Note: if I were using the 236cm doors then the size would be 35mm more ie 1960mm.
The top rail is usually attached to the wardrobe using plastic clamps and clips through the top of the wardrobe. Since the rail is aluminium I just drilled extra holes and screwed the rail to the pine I was using. This is fine for the weight of doors I was using as they have oak veneer panels which don't weigh to much. If I was going to use mirrors then you would need to beef up the fixings!
I hope this has helped. At the very least it keeps a personal record of the measurement I may need in the future if I do this again!
Here is a picture of the other job I did using these doors.