If an elderly relative needs a built-in wardrobe built and you'll be overseeing this construction project, you might find these ideas helpful.
Fit features that will enable your relative to safely utilise all of the wardrobe space
Because people often get less agile as they age and are more likely to have issues that hinder their mobility (like osteoporosis and arthritis), they often find movements that involve stretching upwards or bending down quite challenging. If your relative has reached this stage, you might, at first, feel that it would be best to request that the contractor fit all of the hanging rails and shelves relatively low so that your relative can effortlessly pick up items from these areas, without having to make any potentially painful or difficult movements.
However, this will result in them not being able to make use of the storage space that is near the ceiling. If they have a lot of clothing, this could be frustrating for them. The other solution that you should consider is fitting a feature, such as an integrated, pull-out stepping stool, that your relative can use to safely elevate themselves and easily stow and remove items from the taller storage spaces within the built-in wardrobes. If this stepping stool is integrated (i.e. connected to the wardrobe itself), there will be no risk of it tipping over while you're relative is standing on it and causing them to fall. Likewise, if it is a pull-out stepping stool, then it can be tucked away after being used, and it won't be a tripping hazard or use up a lot of the free space inside the wardrobe.
Fit a small bench in the centre of the wardrobe
If the section of the room where these built-in wardrobe is going to be placed is quite long and there is more than enough space for multiple large wardrobes that will hold all of your relative's clothes, then you might also want to request that the contractor build a small, integrated bench in the centre of the wardrobes. The reason for this is as follows; if your elderly relative is (or may soon become) less mobile, they may find the process of dressing and undressing each day more tiring than they used to.
If there is a bench right in the centre of the wardrobes, they can sit on it whilst they put on or take off garments, instead of having to try to do this standing up (and then potentially getting tired or losing their balance) or having to sit on their bed and then carry their garments to and from the wardrobe.