arma473 has it right. Another way to say it is that: ConsumedResourcesPerSecond = Total Cost / Build Time * Build Rate
Some examples of different Costs per Build Rate are:
T1 Mass extractor:
0.6 (36/60) mass
6.0 (360/60) energy
Monkeylord:
0.73 (20,000 / 27,500) mass
9.45 (260,000 / 27,500) energy
Perimeter Monitoring System:
4.0 (4,800 / 1,195) mass
50.2 (60,000 / 1,195) energy
T1 Mass Storage:
0.8 (200 / 250) mass
6 (1,500/ 250) energy
Strategic Missile:
0.027 (12,000 / 450,000) mass
3.1 (1,400,000 / 450,000) energy
This is how much a T1 engineer (5 Build Rate) would be consuming while it is building these various things (Format is M/E):
T1 Mass extractor - 3/30
Monkeylord - 3.65/47.25
Perimeter Monitoring System - 20/251
T1 Mass Storage - 4/30
Strategic Missile - 0.135/15.5
These are the corresponding build times for a single T1 Engineer. This is just Build Time / Build Rate:
T1 Mass extractor - 12 seconds
Monkeylord - 91 minutes
Perimeter Monitoring System - 239 seconds
T1 Mass Storage - 50 seconds
Strategic Defense Missile (can't be built JUST by a T1 engineer, but if it could....) - 25 hours
You should see that the Cost per Build Rate is totally independent of the Build Time. The Perimeter Monitoring System will use 20 mass / second from even a T1 engineer to build because for whatever reason the blueprint is very fast to build, while the Strategic Missile uses very few resources from any single assisting engineer because the Build Time is HUGE.
Hopefully this helps.
(Data is on https://unitdb.faforever.com/)