In this paper, we commence with the first principles of wave propagation and polarization characteristics during reflection and transmission, and then propose a ray tracing algorithm that can fully capture polarization properties for simulated paths. Simulation results reveal that conventional cross-polarized ratio (XPR) models for multipath components (MPCs), which assume a consistent average value, do not align well with reality. Additionally, the assumption of a constant XPR tends to either overstate or understate the impact of depolarization. This misrepresentation, combined with inaccurate modeling of depolarization in traditional channel models, leads to degraded performance of polarization shift keying (PolarSK) in wireless communication systems. Thirdly, the Average Bit Error Probability (ABEP) performance of different PolarSK modulation configurations is analyzed based on the data from the proposed ray tracing model under various system configurations. These analyses show that indoor building materials with strong depolarization effects lead to irreducible ABEP floors, which cannot be resolved by increasing diversity gain or adjusting constellation diagram. Finally, in order to mitigate these ABEP floors, we introduce an iterative algorithm designed to minimize the floor effect of the ABEP in PolarSK by simultaneously optimizing the complex dielectric constant and thickness of each layer in the multi-layer building material. Numerical results indicate that, for a target ABEP on the order of 10−6, the proposed algorithm achieves a substantial signal to noise ratio (SNR) gain of up to approximately 25 dB, and for different constellation diagrams and different MIMO systems, the ABEP floors are completely eliminated within the considered SNR range, without any SNR penalty. At the same time, we provide a detailed explanation of the physical causes behind the occurrence of the ABEP floor effect. Overall, we establish building wireless performance (BWP) as a fundamental and quantifiable design objective for indoor environments and, by focusing on indoor polarized wireless channels, provide practical design guidelines while revealing that their achievable performance is inherently constrained by building material characteristics and architectural structures, thereby enabling wireless friendly indoor building and channel design toward 6G.