Press the lever. (If you don't have the part, you want to drop one thing again or you dropped something twice, press the number of it's window from left to right.) 1) You can name your building. 2) You can write in the comments what did you drop (and how did you name it).
Once I was playing Bad Piggies and I didn't knew what do I want to make and I thought "I should make a bad piggies build idea maker on scratch". And here it is! options to drop (36 options): window 1: car levitating unit airship plane helicopter rocket hybrid(if you'll drop this, you should drop two more vehicles and mix them) window 2: V2 engine V4 engine V6 engine electric engine window 3: TNT forward missile air missile/ artillery missile falling missile alien cannon bombarding system boxing box alien boxing box alien TNT none window 4: alien engine alien cannon alien blower alien boxing box alien TNT alien lamp alien back rotor alien box alien front rotor alien green bottle alien mini wheel alien blue bottle alien egg alien proppeler alien pig