Sentence 1: The boys had been watching birds all month. 
 Sentence 3: They collected some wood, nails, and a couple hammers 
 Sentence 4:  Then they got straight to work and fit it all together 
 Sentence 5:  Finally they hung it and stood back to admire their project 
 Option 1: Finally they decided to build a bird house. 
 Option 2: Finally they decided to hire somebody to build a bird house.