You may know that I have a Universal USB-1024-14 sign light ballast. Recently, I've decided I want to put it to use. The design is that of a basic industrial strip light, it'll be made of 1/16th in thick metal for the main body and reflector, although a separate flat piece made of 1/8th in thick metal will hold the ballast and hooks and will be connected to the rest of the fixture via mechanical means. I plan on having it operate 4 F36T12/HO lamps, using R17d lamp sockets. Any ideas or suggestions on making this become a reality? I will be designing and manufacturing it myself, but any idea on how to get the measurements right? I want to get the measurements right one the 1st or 2nd time in order to not spend a ton of money on prototypes.

Most CAD software packages have a sheet metal tool that's perfect for this. I believe Fusion 360 and OnShape have a free/reduced cost option for hobby/personal use. A striplight is fairly simple but you can also design more elaborate styles such as louvered fixtures or half pipers.

Some PEM nuts clinched into the sheet metal will make assembly a lot easier with screws and PEM studs clinched into the channel can be used to mount the ballast and as a grounding point.

Once you have your design you can generate drawings with all the measurements and either fabricate it yourself or take it to a sheet metal shop.

Construction metal wholesalers can cut sheet metal and bend it

The bending can be done along a line on any sheet metal part, but bent parts cannot be inserted into the machine again to bend along a line that crosses the 1st bend, only along parallel lines. They use it mostly to make gutters and brackets, in our case it is good for bending the spine, reflector and end bits

Then in the reflector you'll have to make cutouts for the lamp sockets. The construction metal places i know here don't generally have the correct machinery for this job, so you might either want to take it to a more complete metalworking shop (maybe laser), or try to make as much as you can.

In the drawing i show an option how it can be DIY'd. Cut from the edge with tin snips, fold the piece back with long/deep pliers exactly at the line, and fold it flat against the back of the reflector. Though this may make painting the reflector awkward. You may try to grind it off (with a grinder, from the back) after folding. Still do grind it only after folding to not leave a rough edge on the outside

See here for the construction of 90's Gaash 2800, on which you can base the design :

https://www.lighting-gallery.net/gallery/displayimage.php?album=2158&pos=52&pid=108528
https://www.lighting-gallery.net/gallery/displayimage.php?album=2158&pos=51&pid=108529

Use the 4064 reflector shape if you like it more, though for the 2800 based design you'll still want narrow cutouts exactly for each tombstone socket, not wide cutouts like the 4064 :

https://www.lighting-gallery.net/gallery/displayimage.php?album=2158&pos=22&pid=110735

The above strip lights (2800 based on 1600, and 4064/02 based on 5054/02) do have end parts that have precise rectangular cutouts for the tombstone sockets, and are installed in place by elaborate latching tabs. Unless you use laser cutting, you will want to avoid this in the design. (Gaash used press die for stamping it)

Instead, use the design from the early versions of Gaash 1600 with just simple bent parts, however this will require tombstones that can be mounted on a surface (generally the old ones with thick base) and not only pop through cutouts

In the original 1600 the pieces were connected by point welding. You can use whatever method including screws or rivets. (Electrode will burn a hole in so thin metal)

See drawing