Measuring?

I'm just learning how to groom,ride and take care of horses now. I'm saving up money for a horse and I'd like to know how you measure a horse for a saddle. How do you know if the saddle will fit? Do you get someone to measure the horse for you? BTW, I ride Western, so I need to know how to measure for a Western saddle

Please don't reply, I found a sticky with the information I'm looking for:)