A friend would like to make a mezuzah case for me, but has never made one before. Are there any restrictions on its construction or design?
I would argue the following. A mezuzua case needs to be constructed so that the halachot of hanging a mezuza can be followed.
- The casing should have a clear "top", so that the mezuzah can be hung appropriately (not upside down).
- The casing should be taller than it is wide.
- The casing should have an opening large enough for a scroll, so that the scroll can be rolled, and not bent or shoved.
- The casing should not look like some other religion's or religious symbol that is often hung on doors or walls, so that it is clear that it is a mezuzah. (For example, I don't think you could make it into a cross, or horseshoe, or a standard Chamtza)
- The casing needs to be weatherproof so that there is no danger of the scroll getting damaged.
Regarding opacity. In Israel they have a few "standard" mezuza cases, these cases are all the same shape and come in white, black, brown, silver.. AND transparent. So I don't see what is wrong with a transparent mezuza as hudreds of people have them.
It would be a good idea to provide your friend with the dimensions of the actual mezuza you plan on using, to ensure that the cavity inside the case will be large enough to accommodate it without having to compress it.
If it will be exposed to the elements, it must be waterproof and durable.
In addition to the answers already given:
- There must be a way to attach it to the doorpost or wall. So if you don't want to cover it with tape then it has to be lightweight enough, and of a material, that double-sided tape will hold it to the doorpost or wall, or it has to allow nails or something to hold it to a surface.
- The m'zuza (scroll) should not fall out of it when it's upright. Any opening should be made with that in mind. (Of course, if the case will be exposed to the elements, then, as Dave's answer mentioned, it should protect the m'zuza from those elements, so there'll likely be no opening anyway.)
One that comes to mind is that if the m'zuza is within eyeshot of anything disgusting or unbecoming, the case should be opaque so as not to expose the scroll to the unbecoming thing. (KSA 11:18)