GPS - Noise Figure Analysis
You can use Friis cascade noise figures equation. While using the equation make sure to

1) Convert NF and Gain of all stages to Antilog. (You cannot simply divide db/db)

2) Plug in the values in the formula. 

3) Take log of calculated NFsystem.

Below Formula is given for 3 stages,You can extend it to any number of stages required in the same fashion.



For noise floor calculation use
Total Noise(dBm)= Thermal Noise(-174dBm/Hz) + NFsystem(db) + 10*log(Bandwidth).