No need to fret, im probably not relaying myself across clear enough.
Its not feasable to do this from the work menu i would think, its intended as a workshop only design thing unless more detail was added to the work menu to support it but then you in all likelyhood would only be able to create custom tailored clothing to the dimensions of one person because specifying everyone could be indiscriminate work intensive & sloppy when ordered abstractly through the work orders.
Its optional, you can still produce clothes as per normal entity standards but through additional details (like specifying details of images etc on the workshop where the chart would usually be) you have the choice to choose whatever creature on the map for a tailor to take the measurements of to apply to the object.
- Go to workshop -> queue up a job to create a wool tunic, before the job is initiated go into additional details and scroll the list of entities present on the current map to design the clothes on, the worker with or without experience will run out and take measurements, report back to the workshop and gather materials & construct object. Not dissimilar to a artitect visiting a trade depot to design it before letting another worker (or the same) complete the job.
If you do not specify anything it will default to the normal entity size dimensions, and if you repeat the specialised tailor job it won't require a tailor to come out again to measure because it will just carry on replicating the design, similar to how we can repeat images from workshop controls.
I would think that they stack clothes as normal but tailoring could tag more descriptive names ("Dwarf child tunic etc - "It is sized for a dwarf child") by inserting the creature's name in the place of the usual size descriptor as to infer more information to the player, and only creatures who can wear the said clothes would ever claim them, and return redundant clothes to the communal clothes dump stockpile.