What does it cost to build a lightboard?

As described here, about $8K. You can surely economize. (Also consider buying a package from Learning Glass Solutions or Revolution Lightboards; see Buy or Build)

The studio setup described here results in videos with really good lighting, really good sound, and a configuration that presenters can use without technical assistance. Good lighting and sound requires installation, not just purchases. For me, at a university, the value of a room allocated as a studio is so great, that the equipment I put in it ought to be of high quality.

How big does the studio space need to be?

For width, it needs to be ~4 feet wider than your glass board, so that you can angle your lights in at 45 degrees toward the presenter, and yet keep the light fixtures (and their reflections in the glass) out of the field of view of the camera. (See Lighting.)

For depth, let's split this up between depth behind the glass and depth in front of the glass. It's comfortable to have 4 feet behind the glass for the lecturer to move around. In front of the glass, I'd allow about the same distance as the width of the glass, and more if possible. The closer the videocamera is to the glass, the more the presenter develops "monster hands" as he/she moves them toward the glass.

With my 8 foot wide glass, the guideline above would suggest a minimum of 12 x 12 feet. The room that was available was 14 x 20 feet; extra depth is always good.

Why isn't the recorded video left-right reversed, since it is filmed from the wrong side of the glass?

I film with one bounce off a front surface mirror (see the first photo in Electronics.) That makes the video instantly usable, e.g. for live streaming. Some cameras that can do the mirroring electronically (called "scan reversal"), avoiding the need for a mirror. There are other solutions too: see Electronics

Is such a stiff frame required?

Most of the time a less stiff frame would be OK. Stiffness is most needed if you erase while filming, because it is visually disconcerting if the glass shimmies.

Can acrylic, or polycarbonate, or ordinary plate glass be used, instead of low-iron glass (Starphire)?

Not recommended!

Acrylic isn't hard enough. Because of the internal lighting, any imperfection in the surface lights up brightly. Accumulated small scratches from markers & cleaning the board soon become a problem.

Polycarbonate isn't transparent enough. Of course, light goes through a polycarbonate sheet (the thin way) just fine. However for a lightboard we need to get light from the edge of the sheet to the center, through two feet of polycarbonate. It's not transparent enough for that. This is why the edge of a sheet of polycarbonate looks dark grey or black. Compare to the edge color of acrylic (bright white) or Starphire glass (sapphire blue).

Ordinary plate glass is also not transparent enough. Its edge color is dark green or black. The edge color is your indication of the transparency of a sheet when you are considering light that traverses the sheet the long way.

It's hard to clean the glass!

Fluorescent markers do not wipe off easily, as ordinary dry-erase markers do. I find it best to wipe the marks away with a dry paper towel, even tho it takes some scrubbing to do so. Then I use glass cleaner and a new paper towel to remove any last bits of residue. If I use liquid glass cleaner first, the markers smear and I find it's harder to clean this all up than to start with a dry paper towel.

Wet-erase and dry-erase markers, and liquid chalk, can all be erased this way.

Can the lightboard be used live?

You probably don't want to bring in a studio audience, unless you can write backwards or they can read backwards. (However, Matt Anderson has done it: see Illumination in Education.)

I've done a lightboard-live broadcast, where my students attended a live lightboard review session, online. I used Youtube-Live to stream out the video from my lightboard studio. Youtube Live at 1080p has only a 3-second delay. Students typed their questions into a shared googledoc spreadsheet. The TA for my course watched the spreadsheet and picked good questions for me to answer. He typed them onto a monitor so that I could read and begin each new question without pausing. This worked really well.

Zoom is another option with less than 1-second delay. Learn more in this lightboard live streaming guide by Revolution Lightboards.

Can the lightboard be used with Penn State's One Button Studio?

Yes, if you are using markers only, and not any superimposed graphics such as powerpoint. In the latter case, in order to draw on the graphics, the presenter needs to be able to watch their own hand and marker tip on a monitor where it is combined with the graphics. The video processing in One Button Studio is way too slow for this, delayed as much as 30 seconds. In Electronics as described here, using a hardware switcher, the latency is about 100mSec, which is tolerable.