~(으)ㄴ/는 셈이다 = it’s almost as though, I’d say…, all things considered, comparatively speaking, it amounts to

From the verb 세다, this form indicates a calculated result. It is a colloquial expression. 

비싸게 산 셈이다 = I’d say we paid too much.
이 아파트는 값에 비해 넓은 셈이다 = (I’d say) this apartment is large, considering the price.
매일 학교에 가는 셈이다 = It’s almost as though I go to school every day.
서울서 이렇게 오래 살았으니, 이제 나의 고향은 서울이 되는 셈이구나 ⁼ I’ve lived in Seoul so long, it’s like it’s my hometown.

~ㄹ/을 셈이다 = plans to, intends to

나는 오전 중에 돌아 올 셈이었다 = I was planning on coming back before noon.너 앞으로 어떻게 할 셈이야? = What are you planning to do from now on? 
나를 바보 만들 셈이냐? = Are you going to make a fool of me?
유학을 갈 셈이었다 = I intended to go abroad to study.

language.berkeley : korean.stackexchange