what Dr F said. for the one office I do proposals for - we do a projection (proposals that are pre project) and then reports (during/after) with itemized lists of what was actually spent. the sum of the proposal is often different from what was actually spent (which we also have to explain - eg., we projected 1000 $ for hotels but spent only 750, due to choosing cheaper hotel, or fluctuation in exchange rates etc).
for what you are describing, i wouldn't use 5% per person because a construction worker and teacher will be making different $ per hour (i assume). I would write a detail of what is being offered and what work needs to be done, and then for the budget would write something like:
20 teachers at university prof level, a10$ per hour, for total of 52 hours each, total 10040
20 teachers at HS level, at 5 $ per hour, for 52 hours each total 5200
stage one construction (remove moldy material, wall treatment, etc): 10,000
Stage two construction (add second story, flooring, add windows) : 15,000
Stage three construction (paint interior, floor treatment, cleaning): 8.000