Is there a requirement that the landing/porch outside an exterior door needs to be lower than the finished floor?

I looked around and I can't find it.

To my knowledge the code does not “require” the landing or porch to be lower than the finished floor. The area in red is Florida specific which if I recall correctly was placed within so that you could step down one riser.
Is your concern a life safety issue or water intrusion issue?

FRC
R311.4.3 Landings at doors. There shall be a floor or landing on each side of each exterior door.

Exception: Where a stairway of two or fewer risers is located on the exterior side of a door, a landing is not required for the exterior side of the door.
The floor or landing at exterior doors required by Section R311.4.1 shall not be required to comply with this requirement but shall have a rise no greater than that permitted in Section R311.5.3.

The width of each landing shall not be less than the door served. Every landing shall have a minimum dimension of 36 inches (914 mm) measured in the direction of travel.


FBC
1008.1.4 Floor elevation. There shall be a floor or landing on each side of a door. Such floor or landing shall be at the same elevation on each side of the door. Landings shall be level except for exterior landings, which are permitted to have a slope not to exceed one unit vertical in 50 units horizontal (2-percent slope).

Exceptions:
1. Doors serving individual dwelling units in Groups R-2 and R-3 where the following apply:
1.1. A door is permitted to open at the top step of an interior flight of stairs, provided the door does not swing over the top step.
1.2. Screen doors and storm doors are permitted to swing over stairs or landings.
2. Exterior doors as provided for in Section 1003.5, Exception 1, and Section 1018.2, which are not on an accessible route.
3. In Group R-3 occupancies not required to be Accessible units, Type A units or Type B units, the landing at an exterior doorway shall not be more than 7.75 inches (197 mm) below the top of the threshold, provided the door, other than an exterior storm or screen door, does not swing over the landing.
4. Variations in elevation due to differences in finish materials, but not more than 0.5 inch (12.7 mm).
5. Exterior decks, patios or balconies that are part of Type B dwelling units, have impervious surfaces and that are not more than 4 inches (102 mm) below the finished floor level of the adjacent interior space of the dwelling unit.

Thanks Don. This is a question about water intrusion. I was at a friend's house the other day and they asked me why the floor had water damage. It looked like water was being blown along the sidewalk up to the front door and under the threshold. I thought my engineer said they needed a 4" step down to the outdoor landing.
Evidently that is a design decision, not a code issue. He also had a detail that said the finished grade needed to be 6" below the top of the finished floor on a monoslab but I didn't see that either.

I would assume he is attemping to use this section of the 2007 FRC

R401.3 Drainage. Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection so as to not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6 inches (152 mm) within the first 10 feet (3048 mm).
Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152 mm) of fall within 10 feet (3048 mm), the final grade shall slope away from the foundation at a minimum slope of 5 percent and the water shall be directed to drains or swales to ensure drainage away from the structure. Swales shall be sloped a minimum of 2 percent when located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building.

The more I read the more confused I get. This may just be a "coastal" thing but I know the engineer gave me a detail with a 18" deep monoslab footer/slab section, 12" below grade and 6" above. He said the 6" thing was new, it used to be 4" above grade to the FF. I have to admit the whole "concrete" part of the permitting process was confusing to me and it took 4 trips downtown to get my plans through.