How to extract numerical information from text descriptions

I have an attribute that is the description of an operation (i.e description of a building consent), I need to translate this to a mathematical operation. I need to find out the new number of dwelling that is going to build, and I have to ignore any other operation. I am not sure how to tackle this problem. I can do Regex, and do lots of searches but there should be a smarter way (is there???) by using machine learning/text mining/NLP(Stemming and lemmatization) but I am not sure where to start and how to approach this problem.

Below examples show a few cases of the description and the mathematical operation(i.e. the number of new unit):

building of a new unit-1 unit

building of a new garage-0 unit (the garage is not a dwelling)

demolishing of the existing unit and building a new one-0 unit (no changes in the total number of dwellings)

construction of an additional unit-1 unit

destroying the old building and building another one-0 unit (no changes in the total number of dwellings)

divining the land into two sub lots and building two new dwellings-2 units