Accounts Treatment

This is similar to deferred revenue.

Debit cash in assets; credit deferred liability in liabilities.

When you hand over the keys to the house,

Debit Deferred Liability in liabilities; credit revenue in income statement.

In between make another entry:

House Cost is 10,000₹. Advance received is 5,000₹.

Bank 5000

To Deferred Revenue Liability 5000

which means, you received an advance which cannot be treated as revenue as the performance obligation to surrender the flat for consideration has not been met. When flat is completely sold,

Deferred revenue 5000

To Revenue 5000

Complete revenue recognised. I think this is because there is a liability component to provide the service and recognise revenue when all performance obligations are met. It like subscriptttttions. 

Or else, when there is a fulfilled contract:

Bank 5000

Receivables 5000

To Revenue 10000

I forgot the right accounting treatment but its usually, recognise revenue when all performance obligations are met. The first one is better.