How to identify structure/type of model in system identification problem?

Hello, As part of my studies, I am supposed to have a model for building to apply and test many control strategies. Primarily, I generate data using SIMBAD simulink toolbox by creating a prototype for building. After, simulation, it generates data files with all necessary variables like temperature of zones, heating inputs for zones etc. I intend to use this data to identify state space or transfer function model. On this background information, I face problems how to select what type of model structure I shoud use, what order I should specify, the way to calculate delay for MIMO system. I will be greateful for any kind of input to help me with these issues. Thank you very much in advance.

[Andy L]

Can you not check the output data you have simulated? The transient response should indicate a simple model order.