While much has been made in recent years of the Borromean instructions around the shape of the chasuble, many may not be aware that St. Charles gave instructions for basically everything ecclesiastical in his Instructiones Fabricae et Supellectilis of 1577 (which was also translated into English by Evelyn Carole Voelker and published by Syracuse University).
For those interested in St. Charles' instructions around these things, the work is freely available online (see the aforementioned link). To give an example of some of the broader content of the Borromean instructions, here is his commentary on the form of the high altar:
11. HIGH ALTARThe high altar of the chapel can be placed so that from the lowest step of the altar to the railings which enclose it or are to enclose it there is a space of eight cubits or more when possible and if the size of the church requires it because of decorum. This space must comfortably serve the large number of clergy that at times assist at the Solemn Mass and the divine offices. Therefore, where necessary, if at the back of the chapel, outside, there is free space, the chapel will be extended until it has the measurements given above. If this is not possible, and the chapel in the parish or collegiate church is limited in size because of the smallness of the place, then the distance between the lowest step and the railing must be at least four cubits, so that during the solemn Mass, and as required by the ceremonies, there is sufficient space at least for the celebrant priest, the deacon and subdeacon and the coadjutant clerics. The following expedient may be used, if necessary, to obtain this space of at least four cubits in the front part of a narrow short chapel. In other words the steps can be joined to the floor level forming, with respect to this and the chapel, a projection with six or eight sides, that is pleasing to the eye.{1} If there are bays right outside the chapel, and if the size of the church so requires, that same space can be created by extending the wall of the chapel up to the first of these bays. Where lastly, because of the extremely limited size of the place, the space available is practically nothing, it must at least be seen to that the altar is moved much closer to the wall behind it, and if there is really no way of obtaining this four cubit space, care will be taken that the altar is as far from the railings as the site allows, but always detached from the above mentioned wall by one and a half cubits. The height of the main altar will be, from the footpace, two cubits and eight or at the most ten ounces. The length will be five cubits or more, in proportion to the size of the church or chapel, but the width of two cubits and twelve ounces and even more according to the length of the site.{2} Steps of the high altar Moreover, if there is room in front of and at the sides, three steps will be built, and that is one consisting of the footpace and two others below. These last two must be of marble or strong stone, or, if that is not possible, brick. They will be at least sixteen, and if possible twenty or more, ounces wide, depending on the space and in keeping with the proportions. the third step, consisting of the footpace, will be made of wooden boards. The footpace will be two cubits wide, measuring from the front of the altar, and projecting sixteen ounces at the sides, so as to encompass the altar on three sides.{3} The height of each step will be eight ounces. Moreover if, thanks to the size of the church and the high altar, there is room for more steps, five can be built, observing the width and height prescribed above.{4} The location of the crucifix A cross with the image of the crucified Christ will be properly placed under the arch of the vault of the main chapel, in every church, especially a parish church.{5} It will be of some kind of wood, piously and appropriately rendered. If it cannot be set there because the arch or the vault are too low, it will be hung on the wall above the arch, on the outside, below the ceiling, or even above the gate of the chapel railing.
