The SMF recording is an option available in the Defaults table (C1DEFLTS). It can be activated for each Environment, recording can be enabled for security records, activity records, Administration records(1) and Package Administration records(1).
You will have to refer to the SMF record DSECTs, described in chapter "SMF Recording" from the Endevor Administrating Guide, to determine the lengths of security and action records, then make an estimation at how many security and action records are likely to be created for each environment concerned.
Endevor SMF records are written to the SYS1.MANx files and can be extracted to a file of their own using SMF utility (IFASMFDP) - you can ask your system programmer if you are not sure how to do this.
You might want to run some tests - ex. activate SMF recording for just one environment, perhaps one that just the Endevor Administrators use, then extract all the Endevor records to their own file after a certain period to see how much space they take up. Then you can calculate how much space will be needed for a live environment based on the number of users and number of actions they are likely to perform in that environment.