How to make This - :

I’m trying to achieve this Shop but I’ve some doughts
How to cut these holes for Windows.
How to render like this So that it looks somewhat cartoony

Use boolean.
Add a cube and make it clip slightly into your building mesh and make it small to make it the window size you want.
Then select your building and add a boolean modifier
then set your target to the cube you previously made,
And just duplicate the cubes and do the process again for as many windows as you want.
You can apply the modifier and delete the cubes you made.

Now for the cartoony effect you want.
Make sure to use a mate material in principled BSDF, or use diffuse BSDF.
Also if you have some roller shades you can add some subsurface
in principled BSDF
You can add some Ambient occlusion in the Eevee panel too.

You can also extrude the windows inwards by the same amount.

Loop cuts, bevels, and insets would be the way to start out with it. Make your basic shape, add a loop cut in the center where your little trim is, add three loops longways to mark where your windows will be, select those faces, inset individually to get the desired size, then inset again to extrude them into the building.

Your end results should look something like this: