A few quick ideas:
If you can manage to purchase the real estate with just your funds and possibly a non-resourse loan if needed, then let your friend manage the project. Then do vice versa where you manage your friends project that he purchased with his IRA-LLC. This solves the problem of any question about prohibited transactions. You just cannot take any money from the profit of your LLC's project and the loan must be non-recourse. Depending on your experience level, some hard money lenders will do non-recourse.
Also, if you plan to buy and hold vs. fix & flip, you will want to check with a real estate tax accountant. Buy & hold properties have many tax advantages in themselves as the tax code greatly benefits passive income. By buying your property in an IRA, you lose these benefits because you are investing in a tax deductible investment inside a tax deferred account. 2 tax advantages = a tax disadvantage.
Let me give you a rough example: I rent a home that cash flows $500/mo. After the many deductions of owning an investment property I should be taxed very minimally on this income of $500 per month. I may have to pay taxes on $100 per month at the most at the end of the year. A good real estate accountant will be able to find enough deductions to defer most of the income. Therefore you are making $500 per month but really not paying taxes on it. Now if you used an IRA: You would make the $500/month cash flow. This amount is tax free anyways because it is inside an IRA. You now lose out on the deductions allowed to you by owning investment property. You still have the same costs of managing and upkeeping the property but lose the deductions they offered owning it outside an IRA.
Fix and flips in an IRA are a different story because the profits are not passive income and the deductions of fix & flips will not come close to the profit made on 1. Therefore by fix & flipping in an IRA would be a great tax benefit, but you can't touch those chunks of income until you retire.
Sorry for the long and probably confusing answer.