Buying an Apartment

Use “an” before words beginning with a vowel sound.
“Buying” is better here since you are talking about trying to buy an apartment. We would only use “buy” in the title if the purpose of the piece was to persuade people to buy an apartment or if you were discussing some advice you got to do the same.

Apartment prices there range from 8,000 to 12,000 yuan per square meter, but there are few apartments left, and the location of those apartments is not ideal.

“Those apartments” makes more sense unless you had a specific unit in mind (in which case you should have indicated that earlier).

Afterwards, I went to the estate Group of Lifeng and Sun-city.

“Estate Group of Lifeng” sounds like a complete name, and if it is in fact one, you should capitalize “estate.”

There are also few apartments left infrom the Lifeng group, and their prices are even higher than those of China Resources.

“Lifeng group” presumably describes a company rather than a specific site, so “from” is more appropriate.

Sun-city is a newly opened residential building, and its apartments are in plenty of supply, but both the location and the price of their apartments are both not ideal.

Better phrasing

To sum up, among the offerings from the three commercial real estate groups, China Resources is at an ideal price and location, and its environment is very nice.

“Real estate” is always singular.

So, I am afraid that this time I probably won't buy anthe ideal apartment.

This is more idiomatic.