Hi, welcome to AR.
I am glad you have stuck to working out for 4 years, and been patient with your progress. To get the "male model" look (in the far right picture) you do need a bigger and more solid foundation to work upon. IMO You are not ready for steroids, proper workout and diet will get you far without steroids. At this stage, jumping on a cycle will just be a big waste of money.
Would you mind posting your current diet and work out plan to give us a better idea of what you're working with?
With your current physique, a proper "anabolic diet", and banging those heavy weights out on compound movements for another 2 years, you will be surprised how far you can go naturally. At that stage, if your happy with your size, then I'd cut.
Male models aren't that big at all, but they still worked very hard (far right picture) to get their physiques where they are. Patience is key. Remember, Rome wasn't built in a day, and nor was a quality physique.
Don't ever compare yourself with others, whether or not they use steroids etc. Always try to better yourself. Everyone has different genetical potential and capacity, and what's important is fulfilling the potential YOU have been given

Comparing yourself to others will only hinder your progress.