Refactored version of Construction Signaler by codekitchen.
As I kept adding features to codekitchen's version it became a complete rewrite which I'll post as it's own mod here.

Usage:

• Unlocks with circuit network research.
• Place it in the logistics (orange) area of a roboport so it knows where to look for ghosts.

Features:

• reads entity ghosts
• reads tile ghosts
• reads item requests (modules) from ghosts
• reads item requests (modules) from built entities
• reads items required for upgrades
• reads cliff explosives required (can not account for optimization by construction bot logic)
• reads number of logistics cells (can be turned off in map settings)
• optimized performance as much as possible (having to use find_entities will always be a major drain)
• holding a scanner shows logistic network coverage
• Ghost scanners can be turned on and off individually
  Turned off scanners have almost no performance impact (still need to check if it's on or off)

Runtime Settings:

• Update frequency
  reducing scan frequency improves performance
• Scan Result limit:
  counters performance drops during large build projects by limiting how many ghosts are found
  The same mechanism is used in base game for the notification icon.
  Set to 0 to disable.
• Invert output
  saves an inverting combinator when used for LTN requests
• Round to stacks
  Rounds item counts up (down with Invert output) to next full item stack.
  For easiest LTN integration set request stack threshold = 1 and enable both Invert output and Round to stacks.

Known Issues:

• Reading large construction projects with 1000+ ghosts will have major performance impact.
  To counter this scan results are limited to 1000 entities per logistic cells. Setting can be changed at runtime.
• Scanner does not return all ghosts
  Either Scan Result limit was reached (see above) or ghosts are outside the construction area of the logistic network the scanner was placed in.