What are you planning on using for your glazing (or top covering)?

How are you planning on opening your cold frame when it gets too hot inside?

I'm going to assume that you have typical 8x8x16 cinder blocks.

I would probably remove your cinder-block side walls and use plywood instead. I would frame the top of the back-wall and front-wall cinderblock with a 2x8 board. I would then put a piece of plywood to frame the two side walls with a 2x4 sideways to act as "joists" for that angled side wall (near the top). You could use the extra blocks to make your cold frame larger or for another project.

I would then frame the glazing with 1x2 boards with weatherstripping on the bottom so that when it rests on your 2x8 or 2x4 boards you get a mostly weather-tight seal. I would hinge the top and add an auto-lift-vent to the bottom.

If you plan to continue to use your side-walls I would modify your top row so that there are no bricks going forward. This would give you a relatively straight run from the front of the bottom bricks to the front of your top bricks (going up 8" for every 16" horizontal). I would still then cap the ends with plywood and do what I recommend above with 2x8s on the front/back cinderblocks and a 2x4 on the side to support the glazing.

At your discretion you could add 1 or 2 liter bottles filled with water into the holes of the concrete to help stabilize the temperatures (assuming the tops are capped with a 2x8).

I believe your structure gives you 4ft x 2ft floor space. For all this work (and if you go with the auto-vent) you might want to consider going larger if possible. :-)