Your points would be received better without the sarcasm in your opening sentence.
Regarding your point that this tax will be hard to enforce, why do you think this is harder than to enforce than the cornucopia of taxes and construction rules we have today?
Regarding your point about leaving buildings 80% finished, there can be another tax on land not put to productive use. This would include both land left empty, and unfinished construction. In return for these taxes, eliminate other taxes like property tax, stamp duty, registration, transfer of ownership, etc.
Regarding your point that this tax will be hard to enforce, why do you think this is harder than to enforce than the cornucopia of taxes and construction rules we have today?
Regarding your point about leaving buildings 80% finished, there can be another tax on land not put to productive use. This would include both land left empty, and unfinished construction. In return for these taxes, eliminate other taxes like property tax, stamp duty, registration, transfer of ownership, etc.