I have an enclosed porch that was once a patio (I bought the house with the porch). The slab is approximately 13' x 21'. Because it was once a patio the 2x4's on the bottom of the walls are beginning to rot because the slab is 3" to 4" lower than the house slab. The roof of the room is part of the house roof, not an add-on. What I want to do is support the existing roof with 4x4's and remove the walls. I then want to raise the slab of the porch and add approximately 4' x 13' on one end of the slab for a half bath. I will then rebuild the walls to include the add-on. The porch has ceramic tile on the floor. After this explanation, my question is, can I pour concrete over the tile or do I need to remove it? Also, will the weight of the add-on and the extended roof weight be a problem as far a potential for cracking. I am trying to not have the added expense of removing the existing slab if possible, but I don't want problems later.