creating a composite variable?

#1
I am a student doing my master's thesis and I have a question regarding my study. I am working with country data for 25 countries and I am looking into cultural values, attitudes and sociodemographics as predictors of environmental behavior.

For the dependent variable environmental behavior I would like to combine several aspects (Generation of waste, waste treatment, GHG emissions, energy consumption, public transportation expenditure, car usage, env. protection expenditures) Could you please give me an advice how to combine these into one composite variable? If I transform each variable into quartiles (1 being environment protection and 4 environment degradation) can I then add the "rankings" and form a composite? or is this not a valid way to create a composite?

Also, is it a good idea to combine the variables into one composite dependent variable, or should I focus on making regressions for each aspect of environmental behavior separately?

I use the software Eviews and SPSS. Please if I am not clear enough let me know to give further details. Thanks in advance.