New Document and Set Up
Press Control + N in order to create a new document. Adjust the Units to Pixels and set a canvas of 800x650 px. Then in Advanced options, select RGB, Screen (72 ppi)
Go to Keyboard Preferences (Control + K) and enter a value of 1 px in Keyboard Increment. Press OK.
You can activate the Info panel (Window → Info) in order to see a preview of the size and position of your shapes. Remember to set up the measure units to Pixels inside Edit → Preferences → Units. This will speed up your work.
How to Create the City Skyline
Let's start by drawing the background of the city.
Draw a rectangle with a size of 800x650 px (#FFFFCA) on the canvas. Then grab the Pen Tool (P) and draw skyscrapers with the fill color #E8D58D.
Start now by drawing the first building using the Rectangle Tool (M) (#726552). Then create a trapezoid displacing both top anchor points using the Direct Selection Tool (A).
Draw two stripes (#D3C499), one on top and the other at the bottom of the building, then apply Blend (Object → Blend → Make...) with 38 steps of spacing (Object → Blend → Blend Options). Last, make a copy of the shape of the building (Control + C → Control + F) and place the layer on top (Shift + Control + ] ) and apply a Clipping Mask (right click → Make Clipping Mask) with the stripes.
Now draw some illuminated windows (#F9EBC6) using the Rectangle Tool (M). Then using the Pen Tool (P) draw the right side of the building and subtract its shape using the Shape Builder Tool (Shift + M).
After this, select the shape and change its blending mode to Multiply in the Appearance panel with a 50% Opacity.
Finally draw the top of the building with two rectangles (#5B5142) and (#B09C7E). Group the whole building (Control + G).
Let's make the second building drawing three rectangles (#9F8E4D) as steps. Blend them applying Unite from the Pathfinder panel. Then draw horizontal stripes (#D0CBBB) from the bottom to the top of the building, and subtract the shapes using the Shape Builder Tool (Shift + M).
Add illuminated windows using rectangles (#FDFAF1) between the building's floors. Then draw the shadowed sides of the building with rectangles using the fill color (#9F8E4D) and switch their blending modes to Multiply and turn down Opacity to 50% in the Appearance panel.
Finally draw the building's roof using two rectangles (#FFFFFF) and (#CCCCCC)
Let's go on to the third building. Draw a rectangle with the fill color #726552 and then some horizontal stripes (#B8A284) like in the previous buildings. Then draw the roof using two rectangles (#413B31) and (#2C2822).
Last draw the shadow of the other side of the building using a rectangle (#726552) and switch it to Multiply mode and set its Opacity to 75% from the Appearance panel.
Let's proceed with the fifth building following similar steps to the previous ones. In this one, use a rectangle with fill color #7F5936 and color the stripes using #452F1A. Color the windows with #6C4825, and the roof using filling colors #7C6752 and #3F342B.
Finally set the shadow color to the same fill color as the building, its blending mode to Multiply and its Opacity to 50% from the panel Appearance.
For the sixth building draw another rectangle (#BF9F59) taller than the previous building and set the stripes' fill color to #E1D7BF, the windows' color to #FFFFFF and the roof's color to #FFFFFF as well.
Set the shadow's blending mode to Multiply and its Opacity to 50% from the Appearance panel. Last, group the whole building (Ctrl + G) and place it behind the previous building (Ctrl + [ ).
Now in the seventh building draw an intermediate rectangle (#AC8B43), its stripes using color #584B2F and its windows with fill color #F9EDD0. Draw the shadow like in the previous steps taking as fill color the building's color.
Last draw an antenna over the building using rectangles with fill colors #EBB285 and #FFFFFF.
In the last building draw a rectangle smaller than the previous one (#60452A) and draw two groups of vertical stripes (#3F2E1E) leaving a space in the middle of them to separate the front and the side of the building. Then draw the windows using fill color #AB8763.
Then draw the roof slightly overhanging the edge. Use fill colors #A78E75 and #88745F for both sides of the building. Last draw the shadow on the right side with fill color #60452A and switch its blending mode to Multiply and its Opacity to 50% from the Appearance panel.
We've finished our skyscraper, now let's create a giant dusk sun behind the city. For this draw an ellipse and apply a linear gradient using the Gradient Tool (G).
To top it all, draw some clouds out of ellipses using the Ellipse Tool (L) and fill color #FFFFFF. Find the shape with the help of the Shape Builder Tool (Shift + M). Make several copies (Ctrl + C → Ctrl + F) and spread them around the city's sky.
Done! This illustration is quite thorough since we've learned to do a bit of everything and I hope it really was that way and you made the most of it. I hope to see your results soon in the comment section.