Several days in advance, tint 30 oz. rolled fondant gray. If desired, knead 1 tablespoon Gum-Tex into gray fondant. Roll out 1/16 in. thick. With Cutter/Embosser, cut various sizes and shapes of buildings (project as pictured includes 65 buildings); place on cornstarch-dusted parchment paper to dry.
Dust dried buildings with desired colors of Pearl Dust or Color Dust stirred into lemon extract. Add tip 55 ant tip 46 yellow royal icing outline windows. Let dry. Attach sticks to back of 3-5 buildings with royal icing; let all dry.
Tint 4 oz. rolled fondant green. Roll 1/2-1 in. sized balls of green fondant; elongate some into cone/pearl shapes. Indent surface of round fondant ball "bushes" using small end of tip 13; place on cornstarch-dusted parchment paper to dry. With scissors, cut v-shaped "branches" into surface of cone-shaped fondant "trees"; let dry.
Bake and cool completely your favorite 2-layer 8-in. and 12 in. round cakes. Stack cooled small cake layers on same size cake circle. Stack larger cake layers on cake base. Prepare cakes for fondant by lightly icing with buttercream. Prepare larger cake for stacked construction.
Roll out remaining fondant 1/8 in. thick. Cover cakes with fondant. Spray surface of cakes as desired with orange, blue, yellow, red and purple Color Mist to create a colorful sky background. Stack cake layers.
Attach buildings to sides of cakes with tip 12 dots of icing. Insert buildings on sticks into the top cake tier. Arrange bushes and trees.