It costs $60 per half hour either from personal treasury or town treasury to build any buildings in your town.
The percentage of completion of the building you choose to build depends on the factors such as your building motivation and the construction skill points you bring into the job.
At the current stage of this game, because of the above, all of the top towns in each world only get pure builders to build. That gives the town maximum output (or completion percentage) of the building for the same amount of money.
