Light boxes can be constructed in a variety of ways. The simplest to construct is the free standing, horizontal, single purpose light box.
You need to consider the size of the box in terms of surface area. This will relate to the space you have available and the scale that you work at. Having determined the surface area required or possible, you need to think about the height. The top should be of a height so you can stand or sit with a straight back while drawing, cutting or painting. This will vary according to your height and whether you will be standing or sitting. Typically these heights will be the heights of the benches and desks you already use, but you need to check again that you are actually working with a straight back, as this will reduce the fatigue you might otherwise experience.
Note that if the box is going to be sat at, it will need to be narrower to be able to reach to the opposite side. If you will be standing at the box, it can be at least half again as wide as the sitting version. A sitting version will also affect the depth of the box containing the lights. It may not be possible to have anything deeper than 100mm. This will produce some problems with the evenness of the light, but nothing that will make it unusable.
Then you need to consider the depth of the box. In principle, the deeper the box the better diffusion of the light. But there are limits. If the box is really deep, more lights will be required, and potential storage space is lost. I recommend about 150mm for the depth of the box. I then place the fluorescent tubes at 150mm centres across the box. It does not matter which direction they are oriented. That will be more determined by the available fittings and the dimensions chosen.
The flexibility you have in building your own box includes a number of things which could be constructed separately or in combination.
You can cover the light box with a sturdy work board to do all kinds of work on top. So this makes a combination light box and work bench. This top can be hinged so you don't have to lift it off each time you want to use the bench. It should have some support mechanism so it does not fall on your or your work. I have used a chain that allows the board to go back just beyond the vertical. These chains can sometimes get in the way of your work.
In addition to a separate surface the box can be an area of the work bench. The important element is that the rest of the surface of the bench should be at the same level as the light box top. Any variation runs the risk of breaking the glass you may be working on. The cover for this can be hinged to protect the surface when the light is not needed.
Often you will be working on pieces smaller than the illuminated area. It is possible to arrange things so that each light fitting can be turned on and off independently to allow light reduction or intensification as you need. It is simpler to have sheets of opaque card to place around your work area to reduce the extraneous light that will overwhelm the glass that you are selecting or painting, for example. In the case of too much light the glass or the painted lines and shading look darker than they really are as a result of your pupils contracting against the light.
You could add a variation to allow the light box to be used as a near vertical illuminated glass easel. This requires a set of hinges, a ledge on the hinged side and a support of some kind at the back, similar to a piano lid support. This is most useful in painting and in waxing up the pieces to view the whole panel before leading or foiling.You need to think about the amount of flexibility you require the box to have when considering the materials to be used. If you want to use it as part of your display equipment, it needs to be mobile and so relatively light. This will interact with the materials to be used in construction. In this case you may want to make greater use of metals for their strength in relation to weight.
You probably will use opaque acrylic sheet as the surface. If you do, you will need to give it internal support to keep it from bowing. The best for this is another piece of acrylic – clear this time – glued to the top sheet and to the bottom of the box between the light fittings.