Make cuboid outlines and define the top in a different colour
Colour in the outlines with a colour ramp
Make supports in different colour
Add some wires around the buildings in different colour
Make a colour palette or find one (I slightly tweaked this one: Cretaceous-16)
Colour in with new palette (add a highlight along edge)
Add windows
Add greenery
Feel free to change your design as you go along, I initially planned for it to be on a smaller scale but changed it up after realising I liked the city look better! (stage 8)
Isometric is like this if you need a reference. Usually lightest goes on top and the other 2 shades of the ramp can go on either side. If you want to add details on the side remember to follow the angle of the plane.
By copying and pasting a โblockโ you can quickly build up an artwork. Make sure you copy and paste from bottom up as layers donโt exist in the image editor