The house I am looking to buy is half raised foundation and then has slab in the back addictions. I want to level the house and even the floors. The raised portion of the home also has the same level ceilings as the slab, so there are lower ceilings there.
Pedro, I might be a bit confused as to what you're hoping to accomplish with your foundation issue. If I'm understanding correctly, right now there is a crawl space under the original portion of your home and there have been some additions done on concrete slabs. The roof line has been continued across from the original part to the additions without any significant rises or drops, but there is a difference in the floor elevations. So what you're hoping to do is level the floors without disrupting the roof - does that sound correct?
Well, structurally it may be possible, but whether it's economically feasible might be another issue. In order for it to happen, the older portion of your home would need to be lifted or at least supported while the existing floor system and foundation are removed. The existing concrete footings might be able to be used for the new slab depending on their height in relation to the additions' slabs. If not, then they would have to be removed or at least modified. A new slab would then be poured and once it had cured, framing installed to get that portion of the house up to the desired height.
Sound complicated? Well, it would be, especially since a section of the roof would have to be dismantled if the older part of the house was temporarily raised and then repaired when the section was back in place. In addition, many homes on crawl spaces have mechanicals in those areas such as duct lines and plumbing pipes. They would all have to be relocated if that space was gone.
So as you can see, while eliminating the difference in elevation between the two sections of your home may be possible, more than likely it could be very costly. If the lower ceiling height in the original part of the home is an issue and that section is one story, you might be better off raising the roof and just living with the different floor levels. But even that option could turn into a major project depending on the size of your home.
If you're serious about moving forward, my recommendation would be to meet with an architect. They can take a look at your house and possibly arrive at a solution that does the least amount of damage to your wallet. You might be able to raise the ceiling height in much of the existing part of your home without affecting the roof. One other thing to keep in mind is that you want the house to still have an attractive exterior elevation when the project is complete. An architect should be able to help with that as well.