I believe think it is better to exercise in the a gym is better than to exercise outdoors.

I think like that because if I exercise in the a gym, 

I can use various equipment to work out. that I can use.

And I can take classes held in groups if I work out in a gym with equipment. with equipment I can hall the group halls when I do exercise.

And I can also exercise without being affected by the weather.

for the weather if i try to exercise outdoors I can not do it 

when exercising outdoors, it’s too hard to exercise when It is too hot or when it’s too cold.

But, I can exercise refreshingly in a gym at the good temperature.

In the gym because temperature will be quite clear and fresh.

And I can exercise as much as I want regardless of time.

So, For these reasons, I prefer to exercise in the a gym.

-> 주어진 질문에 대한 답변을 잘 해주셨지만, 문법에서 많은 오류가 발생해 전체적인 수정이 필요했습니다. 조금 더 정확한 문장을 만드시는 것이 중요할 것 같습니다. 수고하셨습니다.