I believe what you are asking is the % of homes in a country that are vacant/not occupied
One way to approach this question -
Estimate number of houses
- Look at overall population
- Divide population into number of households (e.g., 3 or 4 people per household on average)
- In a perfect world 100% of households have houses
- Now you can apply discounts as needed - for example, if you are only looking at single family homes then there will be a discount as a lot of people living in cities live in condominiums
- If you are taking all types of accommodation then you will apply a positive multiplication factor as condos tend to have fewer than 3 or 4 people in them
Now you want to look at vacancy rate
- Factors that affect vacancy
- Oversupply of homes
- Declining population
- Aging population
- Net migration
- Urbanization
Look at factors that impact the country in question
- E.g., if it is oversupply you can look at why (low interest rates leading to building boom and ghost towns, or people owning multiple homes, or new towns being built etc)
- Either apply a relevant discount factor to the total homes (e.g., 5% homes are vacant because of multiple home ownership - you will have to have some rationale as to why)
- Or try and calculate what these might be if you have relevant information - (e.g. number of new homes built vs population growth rate)
Hope this helps,
Udayan
(edited)
Master the BCG Potential Test by Francesco 
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