Going from a pretax account to a Roth account means you will incur taxes on any amounts you take out. If you were going to keep the funds in a Roth Ira I would say this is smart assuming you are young as the funds will grow tax free. However, since you plan to use the funds to purchase a home (btw I don't think you will be able to use this for investment property, I would do more research on this if I were you) that would be foolish as you will be paying thousands in taxes in the current year while reaping no benefit as you won't be taking advantage of the tax free growth.
You need to re-think this plan. Messing with your retirement accounts to fund some real estate deal you don't have the cash for isn't very smart. Be patient and save some more. I promise there will be other deals.