Thanks Mongo, that is what I thought. He seemed adept on all other aspects, so I was surprised that he thought that. If his quote is competitive, we will resolve that. I'm not looking for curbless, but maybe more in the 5" or 6" range above finished floor, which would be about the same above the (Kerdi) drain.

First of all, you still haven't specified whether your floor is "not flat" or "not level." Whatever else you have (or have not) done to get where you are, it would help a lot if you could say whether your problem is level or flat. Also, just to be sure here, if I am understanding you correctly, you installed the 2x4s ACROSS the 2x6s that make up the underside of the house? (Notice the very very NON-technical terms...so be aware that I'm not a builder or knowledgeable in this stuff like some of these people that post here...just sympathetic to rising note of panic in your posts....) The only reason I'm trying to clarify that is because I am wondering whether you installed the 2x4s "upright" (so the "4" dimension is vertical) or "laying down". I'm not trying to pile on to what you have *already* done, but I don't know what the proper distance for SPANNING that 2x4s have, and I don't know whether they can span two full feet if they are flat. This makes a difference because you want to install tile. If your subfloor is bouncy or bends ("deflects" I think is it), then all the tile you install will just crack and plague you and your heirs until the end of time...until you rip the whole floor and subfloor out again and re-do it. Or put in linoleum. Whichever comes first. You say in the top post that the cracks are like 1/4", but in your last post you write that they are up to 1". That's a big difference? Which is it? Does it vary from 1/4"-1"? Have you actually measure or are just eyeballing or going from memory? IF YOUR CRACKS ARE VERY SMALL: IF it were me (and it isn't), I'd probably just put down a very tight layer of Wedi board (thinset and screws/washers), seal the seams so it can hold the next layer, then put down a thin layer of self-leveling compound (though you still haven't said whether your floor is wavy or slanted), and then tile. IF YOUR CRACKS ARE 3/4'-1": Maybe use a layer of plywood (which would be cheaper but harder to cut), maybe tape and thinset the seams (ask someone on this board about this because I'm just brainstorming here), then use the SLC, then the tile. Only plywood will actually help form a floor (which I think you need to do with 1" gaps), not backerboard of any kind. Instead of Wedi, you could use probably any backer board (ask someone here what to do for the seams). But I only know about Wedi because that is what we went with, and I like it because it is light weight (good if you are a female working alone). I don't think your solution is in one step. It feels like you are going to have to create a tight subfloor, THEN level or flatten. I think you have a non-standard thing going on there, and that might not be addressed so easily with just one step before tile. One more thing, just out of curiousity, WHY do you think your floor must be level? Oh yeah, and I would start making your peace with a threshold. Given how non-standard your set-up is, AND the fact that this is DIY (or at least the subfloor), I'm not sure it is realistic to think you can get away with no threshold.

A structural engineer could design a floor system that is only 8" thick. Some possibilities are: a flat plate slab floor, a metal deck and concrete composite floor, or light weight steel. Or a 10" thick floor with 1 3/4 x 7 1/4 LVL's and a 7'-10 ceiling height. But if you check the zoning ordinance I suspect you will find a 2 1/2 story limit unless you are in a multi-family zone but then the building height would probably be higher.

How much of an issue is the puddle? Does it cause a hazard when walking to your car? Does it cause damage to your property (the stuff stored in the garage)? Do you 'need' perfection or is a DIY patch (and an obvious one) good enough for you? When it comes to leveling concrete it can be easy (assuming you have been taught some tricks of the trade AND have worked with the SLC product before) or it can be frustrating (none of the above). Technically you can rough up the concrete (give it a deep clean with detergents...then rinse, rinse, rinse and rinse again). You can prime it. Both of these are pretty easy. The tough part is the SLC. It is not self-leveling and it can be tricky to get the mixture right. Remember: SLC have MAXIMUM thicknesses as well as MINIMUM thicknesses. You have to choose the correct SLC AND IT'S OWN PRIMER to do the job properly. You have to know the max/min of the product and you have to leave an edge that you grind down later. As an aside, epoxy coating isn't going to do anything for the dip. Epoxy is a coating. It isn't a 'build up' product like SLC. To fix the dip, the epoxy professional STILL has to fix the dip with SLC.