Stick a 4X4 plate up on the wall and cover it randomly with tiles of various colors. That makes great modern art.

You for sure want to adjust the lighting so it looks smaller than it is. The shadow from the wall looks terrible, but that's probably not gonna happen for final shot. But adjust the light so that it doesn't look like a facade.

I wouldn't add a random stripe on the wall. How many interior walls in houses actually have stripes like that?

Instead, I would consider your framing and composition a bit more. I understand this is a set/prop critique thread, and not a cinematography thread, but I'm assuming your second image is a test shot.

I assume the figure reading the book/newspaper is the focus of this shot. If your camera can handle it, I would move the camera in a bit closer and move it down. Don't TILT the camera down, move the whole camera down. This probably means you will need to raise your set.

I've often noticed in brickfilms that the camera is pointing downward toward the characters for no cinematic reason, which I find to be distracting. Generally this is probably because most brickfilmers build their sets on baseplates that are placed directly on their animating table. This leaves the set very low to the ground, and most webcams can't get any lower and still be on the table.

In most films, the camera is roughly at eye level by default. This puts the audience at level with the characters. I think greater effort should be put into trying to mimic this camera positioning, even if this means building your set with stilts.

Hope this helps!

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GEF keep the yellow.  Nice rustic appearance.

Seems a bit too plain to me. It's got just the one basic, fairly small, building behind the platform, and that's about it. And the sky isn't that blue. (Although if it's supposed to be that gray, that's fine.)

The holes in the top piece also betray the real scale, and hurt any forced perspective effect. (The non-tiled studs also do the same.)

Now, I'm certainly not saying that my rooftop is perfect, (Since it's not) but perhaps you could draw some inspiration from it. Or perhaps a better idea would be to examine the rooftops of the Modular Buildings. Those tend to be fairly plain, but generally contain a couple of cool details like a water tank, a skylight, or something else of interest.

If you do want to go with the stark, minimalistic look, I suggest just making the background building extend all the way across the frame. It may convey the idea of a balcony more, but I think it would go nicely with the idea.

Here is a picture of my set

What do you think? I really need your critics and ideas, because I want to improve in set designing.

There are actually walls in those rooms. You just can't see them because it's too dark in there.

Oh, never mind then

Nice clear picture. It seems kinda bare to me though, perhaps adding a few pipes or perhaps a vent, or trashcan, just something to breakup the flat bare surface. Being able to see an edge to give that "raised platform" feel would also help. Nice rooftop doorway, and good luck on the film.
What I do to make the sky even is to move the darker edge of the blue-screen (or in your case, a shirt) closer to the light.