A woman buyis buying a skirt and read with the shopping assistantis talking with an employee.

"is buying" or "buys" is the correct form you want here, since this is a conversational excerpt.

"read" is the wrong verb to use here, it should instead be "talk" or "speak".

"shopping assistant" isn't exactly wrong, however using "employee" is much more natural sounding.

SA;: We have skirts very much which age.very many skirts. What size?

You want a colon (:) here instead of a semicolon (;) -- just a small typo to watch out for.

"very much" cannot be used unless used here since "skirt" is a countable noun. Here instead you must use "very many" instead. Although, simply "many" also works and is probably preferable unless one really wants to emphasize the quantity.

"what" vs "which" is complicated, but here either works. I would say that "what" is probably preferable.

W;: I havewant a size 12 and one that pleaseis very wide, please.

"have" would be for what she is currently wearing, you want to use "want" or "would like" to indicate that it's a request. Alternately, she could ask for a "wide size 12". The woman could also (assuming she was buying the skirt for herself) simply say "I'm a size 12, wide" in this instance

SA;: Oh, we werehad a size 12 but now we do not .

"were" would not be used here, instead use "have" (past tense 'had').

The "a" here specifies that the particular skirt in that particular size is out of stock, if it were omitted the sentence could be construed as the store having no clothing in size 12 at all (although, that probably wouldn't be the case, so you could realistically could omit it here)

W;: Ok, then please give me a size 13, small.

The "please" is just to be polite, not necessary, but recommended!

Typically, you should use an article "a" when talking about clothing sizes

SA; Good: Alright, which color.?

"Good" feels like a strange response here, "fine" would work (although, that makes the employee sound rude to me), so instead "alright" sounds the most natural here.

W;: I would like a in blue and purple skirt, please .¶
¶
OR¶
¶
W: I would like a skirt in blue and purple, please.

SA;: No problem, the changing rooms are behind you.

if using "are" then the noun here must be plural "rooms".

"behind" is used prepositionally here and therefore a more specific phrase with "you" needs to be used here. Here specifically, the changing rooms could be behind *anything*.

W;: OK, I will wait there then.

Saying "I wait there then" gives it a strange sense e.g. "I was going to wait over there, but now I will wait over there instead"

SA;: Here areis your skirts with a blue and purple pattern.

"Here are your skirts..." is correct, however the past conversation only established a single skirt, so plural doesn't 't make sense here.

W; what: How does it look like.?

"what does it look like" is a valid question, but in this instance would only make sense if the woman was blind. Instead the phrase "How does it look (on me)?" should be used

SA;: It look likes great and is very beautiful.

"like" isn't needed, and "look" needs to be in 3rd person here "looks".

W;: How much money.does this cost?

"how much money?" wouldn't be used here, maybe you could say "how much money does this cost?" but that's overly specific since the "cost" here is assumed to be currency and not labor or barter.

"this" or "it" both work fine, I'd personally use "this" were I wearing it or were I to have it in my hand, but that's not exactly a rule.

W;: Goodreat, here is your money .

Again, "good" as an emphatic start to a sentence just comes off as rude or stoic, I'd use "great" or "alright" instead.