Parking is simple math.
100 cars enter every day
100 cars leave.
there is space for say, 80 cars
As one exits the lot, there is a new space available. (simple math)
an arduino in every space can say there is a car there (or not)
all report back to a central point.
say 5 cars enter and 3 cars pull out and drive to park out of the sun,
none leave the exit, so available spaces are total , less occupied, less cars not in spaces
every arduino that shows and empty space would light green on the map as available.
it's really not rocket surgery.
however, I get the feeling the OP has no experience so needs to hire people to do the work.
I think we are writing the basic spec's for the project.
as I see it ( by NO means is this perfect )
arduinos to detect car in spaces, needs some means to report back to a central computer
license plate auto-scanner and entrance and exit, probably a Pi due to more software than ESP32 (the other micro that does camera recognition)
central controller, web host and sign control.
all space devices report back arduinos report occ or not occ
plate scanners send time and data, in or out
central controller , posts number at entrance '27' available spaces
central controller, hosts website for map
If one wanted to know what plate went into what space, then a camera in each space for plate scan could replace Arduino to detect if space is occ or not occ
weather harden
all units need to be hard cable networked for power and data
all enclosures need to hardened for vandalism
speed of completion is based on the size of the team.
software for lot full is easy, would be able to help with that in this group
** premium paid service. buy a space in advance. pay extra.
** cone to 'pop-up' to show reserved and goes dark on the map. also reduces available count.
once you add features, time and money influence outcome.
plate recognition
space sensing (not the same as counting in and out of cars)
enclosure design, circuit board and sensor design
*sensor field testing
power data network design
website design
any one of these could take months.