ventilation: air in from under the door, air out through the vent in the ceiling
Either the garage door would need to be cut and adjusted in height to conform to the floor, or the floor would need to be modified to conform to the door. If the door bottom is near level, the floor should be built up to meet the door. If the floor is level, there are serious issues with the door. Consult a garage door installer.
Doors usually have a small gap between the bottom of the door and the floor, and in most cases, it is possible for a piece of paper to fit through that gap. So even if a door is locked, you can still deliver a piece of paper.
the expansion gap is suck your mum
Ceramic tiles have a grout "gap" but vinyl tiles shouldn't have a gap.
Lag
It may be your outside window scrapers. Look for a gap between the door windows and the rubber scraper. If it is missing, torn, or worn out, it will let water into the door. That, in turn, will allow water to get on the floor. Inspect the bottom panel of each door. If it appears to be leaking water, open the door and shake it back and forth, listening for water (if it's been a while since it rained, wash your car). Performanceproducts.com offered replacement parts for W123 cars.
main purpose is cover the gap of door and window frame and wall and decorative of door and windows
There is no standard. Flooring type and use of rugs over existing flooring are the deciding factors in choosing the space to leave at the bottom of a door slab.
More info would help. However the most comon problem is settling of the subfloor framing causing the wall to also settle. This causes the crack in the drywall and commonly the door to stick. Close the door and look at the gap between the door and the casing/frame the gap should be the same size on each side and the top of the door. If the gap is not the same, settling or a poor install of the door has occured. Inspect under the house -girders, joists and subfloor for settling rott, and termite damage.
Because as tectonic plates move away from each other, the ocean floor spreads apart and fills the gap.
All of the Mopars I've worked on (225s and 318s) use a gap of .035"
No gap is intentionaly left. Your squeaking will be between the subfloor and joists.