Builder's shirt is obtained during the Tower of Life quest. This item is part of the Builder's outfit.
After completing the quest Tower of Life, the Builder's outfit is not necessary to enter the Tower of Life and may be destroyed if wanted. A new set can be obtained within the Tower of Life. If you have destroyed or lost your builder's shirt, talk to 'The Guns'. He will tell you he wants you to go to Yanille and buy him a cheap beer and then you can get your shirt back by talking to him again.
• • • • • • • •