/fileLogger[n Logs the build output to a file. By default the file is in the current directory and named "msbuild[n].log". ...

/fileLogger[n]     Logs the build output to a file. By default
                     the file is in the current directory and named 
                     "msbuild[n].log". Events from all nodes are combined into
                     a single log. The location of the file and other
                     parameters for the fileLogger can be specified through 
                     the addition of the "/fileLoggerParameters[n]" switch.
                     "n" if present can be a digit from 1-9, allowing up to 
                     10 file loggers to be attached. (Short form: /fl[n])