Floor slopes are a red flag in the TREC SOP. I do not think that sloping floors are a particularly useful red flag. In my opinion, sloping floor slopes are the least reliable and least useful red flag in the TREC SOP.
Why do I say that? Sloping is almost dead certain to develop to some degree even when the foundation is performing within the intent of the engineer who designed the foundation. That is not true of the other red flags.
The other red flags
Binding, out-of-square and non-latching doors
It is highly unlikely that any buyer of a new home would fail to make a builder correct such doors or that a builder would refuse.
Normally, doors that do any of the above are in a wall that is racked. For doors on the ground floor, the cause is usually foundation bending. For doors that are on a second or higher floor, the most common cause is framing. You will see this in many two and three story homes that are 10 or more years old.
Framing or frieze board separations
There is almost always some degree of framing and frieze board separations. It could be due to sloppy workmanship or to foundation bending. The more severe it is, the more likely the foundation is the cause.
Window, wall, floor, or ceiling cracks or separations
Here again, there are multiple possible causes of drywall cracks. When the foundation bends, the first story walls are racked. This results in diagonal stress patterns. That stress, if it is severe enough, can cause diagonal cracking in the drywall, especially at the corners of window and door openings. The corners of these openings and geometric discontinuities that create stress concentrations. This is why foundation related cracks are usually found at these locations.
Drywall ceiling cracks are usually due to framing issues or age or both. It is difficult to understand how a foundation could cause ceiling drywall to crack, but not the drywall on an adjacent wall.
Floor tile is usually very brittle and will fracture with even minor foundation bending. If the crack goes from one tile to another, the cause is usually the foundation, especially if the tile is bonded to the slab surface. For tiles that are bonded to the wood subfloor, the cause is almost always a lack of adequate stiffness in the subfloor.
When the finish flooring is wood or a wood product, foundation bending can create separations between the flooring pieces.
Rotating, buckling, cracking or deflecting masonry cladding
These types of distress in the brick veneer may be caused foundation bending among other things such as missing or inadequate brick ties and under-sized lintels.
Brick veneer cracking and separations are usually caused by foundation bending, although that is not always true.
Of all the red flags or indicators in the TREC SOP, the least reliable is floor slope. Of all the TREC indicators, floor slope is the only one that is often built-in. No builder that this engineer knows of is so incompetent that he or she builds houses with drywall cracks, sticking doors, brick veneer cracks, or any of the other indicators. Even the most quality conscientious builder builds slab foundations with measurable slopes.