This script looks for changes in Dropbox folder. Upon any change, waits for the status to be Up to date. When it's fully synced, starts a build process (/app/build.bin).

build_after_dropbox_sync.sh

#!/bin/sh

uptodate () {
  # returns 1 if up to date, 0 otherwise.
  python /root/dropbox.py status | grep "Up to date" |wc -l
}
build_after_uptodate() {
  while [ "$(uptodate)" != "1" ];  do
    sleep 1
  done
  echo "Build now!"
  /app/build.bin
}

while true #run indefinitely
do
  if [ -d "/root/Dropbox" ]; then
    inotifywait -r -e modify,attrib,close_write,move,create,delete ~/Dropbox && build_after_uptodate
  fi
done