Hey fh -
Self leveling is pretty easy stuff to work with. If you prep right, it won't be messy.
Keep in mind...NONE of this stuff is rocket science. And you CAN do it. Maybe not as fast but you can do it. Having said that, it also depends on the particular job. The real question is...do you really want to do it, or are you wanting to save yourself a buck. Like I said, if you are more interested in trying to save a buck, I'd probably have a floor/carpet guy/gal come out to do it. Fairly routine for them, they will have the right tools and they will knock it out rather fast and it probably wouldn't cost that much. But get an estimate, then price out the materials if you do it yourself and if the difference is significant, give it a shot! If not, let the pro do it.
If you really WANT to do it (I do enjoy doing this stuff, so it is not so much of a money saving thing for me. Sometimes smaller jobs, after you buy all the stuff you need, may not save you that much, so it becomes more of a fun project). Buy a video or book on flooring. They all have pix on how to put down self leveling concrete. It really is pretty routine. Mix it in the bucket to specific consistancy, pour out a small amount and trowel it smooth feathering the edges. Do all the prepwork before you get started. Goggles, gloves - rubber medical type, hat if your hair is long, knee pads, old clothes, 5 gallon painter's bucket, drill with a long mixer attachement, trowel and your mix. Pull up your carpet, roll it up, mark where you started. Run a string from one corner of the floor diagonal to the next. Find something like a cinderblock (or someone) to hold it down to the floor in one corner while you hold it down on the opposite corner. You will see the dip. Walk up to the point of the dip that is closest to you. Take the string in your hand (while the other end is still secured) pulling it taught and leaving it level to the ground. You should be holding the string down on the outer edge of the low spot. Then begin dragging the string across the low spot from left to right marking the perimeter of the low spot. Thus you will draw an outline around edge of the dip. I know this sounds like a pain, but this will take about 5 minutes. Once you outline the perimeter of your low spot. Mix your concrete, then pour the concrete in the center. Let if flow out naturally. Depending on the flowability, if it is a little thick, you may need to trowel it outwards from the center to your perimeter lines. Lightly drag the trowel from the top of any high spots pulling the concrete to the perimeter. Start out pouring less until you get a feel for the area, the viscosity of your mix, where the concrete flows, etc. You can always add more concrete. Keep in mind it should flow more than you will have to spread. But if not, no big deal, just spread with your trowel. Once it is smoothed out and level by the naked eye, and it begins to harden slightly, do your string test agian. It doesn't have to be perfect, but if its within about 1/4" to 1/8 of inch, you will be fine. Then walk away and let it dry. Once dry, roll the carpet back over and you are done. Now, I have never tightened carpet but again...it ain't rocket science. But read up on it first.
Remember, if you pour too much too soon, it may naturally spread beyond your perimeter lines so start out with a small amount. Let it flow naturally to test then use the trowel to spread. It may result in you spreading beyond your original lines. But that's ok.
Like I said, I enjoy some of this stuff. But, if the cost to have someone else to do it is within your budget, get someone to do it.
Let me know how it goes!
BTW, I hope this makes sense! It really is pretty routine. Especially since you have a specific low spot.
Hazen