Sorry for the long preamble...I see from many postings that I share the same issues or concerns, only mine is in concrete. I will be glueing 3.5" engineered hardwood throughout the home. We cast radiant heat lines in 2" concrete and the retired floor finisher should have never entered the business. What a mess.

As it is a new home with open areas, I am using two 12 ft straightedges - a 2x4 and a 2x6. When I place them across the floor in some places the straight edge (SE) touches in two, three or four places or the end can be sticking up 3/8". I have a 3/16" shim that in places I can slide it clearly under the SE. Yet when I turn the other SE at 45 degrees, or slide the SE further down, it can be flat to the floor the whole distance.

Most advice I have received is get the self levelling floor leveller compound but it is crazy expensive. We had a professional place 700 sf of tile and he used Mapai. His bill for the self leveling was $4000 ! ! ! In addition, this planipatach?? does not feather.

Worse yet, on the main floor I asked him to prep a small area in the hallway so the transition from the tile floor to the hard wood would be better and to stop it at an identified high point. He used a block to control the self leveller and when dry, it actually INCREASED the height of the highest point!!! This now increases the variance to the open area of our LVG rm an DNG Rm. To use self leveller for this amount over the remaining 900 sf would be totally cost prohibitive for the amount required. Repouring because of door openings and finishing is not an option. We are in a remote area and cannot access even specialized pumper systems. We need to DIY.

To make the floor FLAT within 10' I am thinking of just filling in the low spots to the point that my 3/16" shim will not slide under my SE. To add to the challenge in the livingroom...I have 3 floor outlets placed in the sitting area.

CALLING ALL EXPERIENCE... does anyone have any cost effective ways of dealling with this? What are some options? As to the concrete finisher...murder is NOT legal.

You are biting off too much on the lengths to check. I think you would be better served to use a 6' or 8' straight edge and map out the floor. High spots and low spots.

Take down the high spots first and then map the floor again re-verifying the low spots. Planipatch is what I use to fill those and I feather it without any problems.

another suggestion may be to use : Self Leveling Cement... Grind the high spots and float the floor with self leveling cement. It will add thickness, but only about 1/4" and less.
The floor will be flat and smooth and it will do it by itself, if properly applied.. BUT:: it depends on the PSI strength of the existing cement used as you cannot place 3500 PSI over 1200 PSI.. the PSI must be within 500# of each other as excessive differences in PSI strength results in cracking as the two cement strengths have different properties such as movement/shrink/swell...