I just spoke to a client about Leasehold Improvement Exchanges (LSH), also known as Advanced Build to Suit Exchanges. They are a very powerful tool for the taxpayer that already owns the property to be improved. The downside is there's an element of risk involved that cannot be eliminated. The LSH is derived from Private Letter Rulings (PLR) and can only be directly relied upon by the taxpayer that sought the ruling (s). However, the broader public may use these PLR's to gain insight to the Service's thought process regarding these types of exchanges.
These are very complex exchanges that when done correctly can minimize a number of risk factors, but will not eliminate them all. Be sure to work with an experienced Qualified Intermediary and tax advisor if you are considering one.