This is a small display case consisting of two halves:

the bottom half shaped like a tray, with four additional vertical pillars,
the top half with the glass plate.

The two halves fit together, thanks to the pillars, without needing any hinge nor latch.

The motivation to build this display case from scratch came from several reasons:

After envisaging buying two picture frames, it turned out that (1) I could not find frames that are thick enough, (2) frames made in China means kerosene, (3) I cannot get the exact size I want, and (4) it would cost 2 X 20$ for wooden frames of nice quality.
I had remaining wood from a former project. So the cost is just the glass (approx 8$) and the investment for a router bit to make the grooves (20$)
Building from scratch is more fun!

Step 1: Needed Stuff

Materials:
As said before, I had remaining wood from a former project. But the list is pretty simple:

Wood bars. Preferably hard wood (beech, oak, etc.)
MDF or plywood plate, e.g. 5 mm thick
Glass, 3 mm thick. The best is to measure the needed size at the end of Step 3. Ask the shop to cut it to size.
A few screws and dowels
Wood glue (modest quantity)
Linseed oil (modest quantity)

Tools:

Saw or electrical jigsaw
Sand paper, sanding machine (or sanding block)
Framing vise (optional)
Router and router bit for 4 mm wide groove

Step 2: Cut Wood to Length

To get 2 frames:
- 2 x 2 x long bars
- 2 x 2 x short bars

For the pillars:
- 4 x shorter bars

The bars that I have (from a former project) have a particular cut. I used this cut as a recess in the frames corner, for the pillars.

Step 3: Assemble Frames

Assemble each frame, optionally with the help of a framing vise for best alignment.

Use dowels and screws. Drill holes for dowels, pre-drill holes for screws. Glue the dowels into the short frame sides, by means of a drop of wood glue.

Mark each piece with a pencil in order to remember their ordering.

Measure the required size of the board and glass plate (taking the groove's depth into account).

Disassemble the frames for the next step.

Step 4: Make Grooves

Make the grooves with the router. Use a bit for 4 mm wide and 10 mm deep grooves.

WARNING! a router is an extremely dangerous tool. It rotates much faster than a drill, and can cause nasty wounds.
- Wear protection glasses and work gloves
- Tighten wooden parts in a very stable vise
- Hold router with both hands
- Exercise on some scrap wood

Step 5: Sand and Oil

Re-assemble both frames.

Sand the joints for perfect alignment. Sand chamfers wherever wanted.

Apply linseed oil.

Step 6: Cut Bottom Board and Top Glass

Cut the board to required size.

Step 7: Assemble Bottom Part

Insert the board into the bottom frame.

Remount the frame, secure it with screws.

Place and adjust the pillars, secure them with screws (pre-drill holes).

Step 8: Assemble Top Part

Mount the top part: assemble the frame with the glass. Secure the frame with screws.

If necessary, sand the corners so that they fit "quite freely" into the pillars.