Not native, but I do have conversational fluency so since this is a simpler question I'm confident this is right: 1.저은 집을 있이요 - I have a house. >>저는 집이 있어요. 2.저은 복장를 없에요- I do not have a dress. >>저는 복장이 없어요. With 있다 and 없다, as stated above in a comment, you never use the object particle (을/를). You always use the subject particles (이/가). It is a harder concept to get over when going from English to Korean when you think "I *have* a house," but instead you should think "For me, a house (of my own) exists." Also, make note of when to use each particle. Since "저" contains no consonant on the end (as in the if you sound it out, there is no consonant sound that ends it, but rather a vowel "Jeo"), you must use "는". "은" can be used if the syllable ends on a consonant. When a character ends with a consonant, so to speak, this, in Korean, is called 받침 "baht-chim." This also goes for the object identifiers, etc. So if you were to use 복장 in a sentence where it is the object, you must use "을" with it. For example, 오늘 저는 복장을 샀어요 - Today, I bought a dress. Hope I answered anything you might be confused about.

Thank you both.

있다 and 없다 are like adjectives and so you need to use the subject particles for house and dress and not object particles.

Not Korean but... 저는 집이 있어요 저는 복장이 없어요. maybe? Although, maybe you would want to use the word "own" 소유하다 when talking about having something like a house.