@Cory Adams Moving funds between banks within a 401k is not at all like a rollover.It sounds to me like you are thinking you can use those funds for your bridge loan, and that would be a prohibited transaction.Speak to your plan provider and or your attorney before you fry your 401k savings.

@Kevin KlaasIRS rules prohibit any direct or indirect benefit between an IRA and a disqualified person such as you or lineal family.There is no means to mix IRA funds in a property you wish to use personally in any way.Your IRA could joint venture with or lend to an unrelated investor on a deal they are doing.

@Jay Kaltenbach In my opinion, the best investments to make with self-directed IRAs are those that are least likely to result in a prohibited transaction. 

Even after the market crash, housing prices in the city tend to be prohibitively expensive while rents are low.

I like how the front entrance has at least 3 separate signs prohibiting loitering.

Many condo associations have building rules that prohibit renters.

The IRA can invest in real estate in addition to or instead of just stocks.Because the IRA is tax sheltered, there are strict prohibitions against any kind of self-dealing.  

So, typically, you will find that many of the applicants looking at a shared unit situation are doing so because there is some qualifying factor that is likely prohibitive of them being able to rent their own studio or 1/1(income, credit, etc).With that said, I am sure that you can find enough qualified tenants to fill your property.

Also, it usually makes a difference if you're renting out your entire property or just a portion of it (like a room or a guest suite), normally you can do this right away assuming that your local government allows this (municipality, county, HOA, etc..) and there are no deed restrictions prohibiting it. 

IMO, there is nothing that would prohibit a private buyer and seller from structuring a contract this way.