How to develop the correct database structure?

Question

Database

It is required to develop a software package for housing and communal services.
I roughly understand that it should be done on the basis of Redmine.
You will need to write your own module.
Development in ruby ​​will be transferred to freelance.
How to describe/develop the database architecture in such a way that you don’t have to redo it later or hit the ceiling, because Was the structure initially designed incorrectly?
ZYZH since the project is non-commercial, social, the solution should be budgetary or even preferably free. advice to hire an architect is not suitable - it is unreasonably expensive.

Answer 1

Impossible

Answer 2

Start simple - select objects - "users, user groups, houses, tenants, commercial offers, suppliers, etc."
Then you endow them with properties:
the user has his own login, password, access level to the database (group ID) ...
All this is done with the participation of the customer, find out what he needs, he signs to exclude "let's add more ... "
Then, without a customer, build relationships:" There are several apartments in the house. The housing and communal services office has several houses.
And remove duplicate properties. Supplier A has its own email address, in the commercial offer of supplier A there should not be email.
Then you think about the extraction time, if you need to make a complex query consisting of 10 tables to select, is it not better to duplicate the properties in two or maybe three tables? Find a balance -)
and little things:
You write down all properties as fields, in the same place you write the names of keys and foreign keys. Then you think over various details - auto-numbering, auto-completion, but this can already be corrected in the course of the play.