Redmine

Issue Custom Fields Parent/Child:
I am a newbie trying to do this requirement. I could not make it work by just using the plug-in. It seems like many of details solution is within the Redmine core. HELP!
Our project requires the use of Issue Custom Fields model a parent/child type relationship. Currently, there is no facility to define both Parent and Child as entity classes with a < bidirectional one-to-many> or mostly < bidirectional one-to-one> association with cascades to model a parent/child relationship. A very simple example is;
Building [Main, Engineering, Production, …]
Has Floor [1, 2, 3, 4, 5, 6, …]
Has unit [1, 2, 3, 4, 5, …]
Has room [bedroom, washroom, dining, …]
Has flooring [hardwood, carpet, cement, …]
The chain of parent-child will look like this:
Building (Main)  Floor (1)  Unit (101)  Room (living room) Flooring (hardwood)