• It cost 70% less to construct than a normal building.
Which view is grammatically correct to evaluate the role of above to infinitive – to construct – between following two ;
1. it; preparatory ‘it’, to construct; extra subject. In this case, the original sentence of above before abbreviation is ‘It cost 70% less to construct than (it cost to construct) a normal building.'?
2. it; empty ‘it’, to construct; adverbial to modify the verb ‘cost’.
Since I feel this sentence seems tricky, I would like to be advised various opinions. At moment, I have no additional context as it stands only.
Thank and RGDS