hi
...indoor propagation is very dependent on a lot of parameters like: frequency, signal bandwidth, Tx-Rx distance, LOS or NLOS conditions, ...etc.
There are some models available on a lot of IEEE papers, basically grouped in Statistical models (based on statistics of measurements) and Deterministic models (based on ray tracing).
Deterministic models usually takes into account the EM properties of the objects that obstructs the signal, so maybe you need to look for this kind of models (the one that better adjust to your needs). Search on ieeexplore and citeseer.
for example, take a look to this paper:
Prediction and Measurement of Wall Insertion Loss
Thad B. Gibson and David C. Jenn,
IEEE TRANS. ON ANTENNAS AND PROP. VOL. 47, NO. 1, JANUARY 1999
pp 55-57
hope it be helpul
regards