Why あります instead of です in this sentence?

Question

In the following sentence (from here),

北海道札幌市の円山動物園に、ミャンマーから来た３頭の象をみんなに見せるための広い場所と建物ができました。[...] 広さは５０００m²以上あります。

I would have expected です instead of あります: 広さ = ５０００m²以上.

Answer 1

「広さは５０００m²以上あります。」

is a perfectly natural-sounding sentence.

「あります」 can be replaced by 「です」, but that will change rather drastically the basic grammar (if not the meaning) of the sentence.

In the original sentence, 「５０００m²以上」 functions adverbially to modify the verb phrase 「あります」. As discussed in this Q&A, number-related phrases can function adverbially in Japanese. From my own experience with Japanese-learners, however, they seem to have difficulty getting used to this concept.

It is more natural (or more "originally Japanese") to say:

「リンゴがむっつあります。」 ← 「むっつ」 functions adverbially.

than to say:

「むっつのリンゴがあります。」 ← 「むっつの」 functions adjectivally.

Thus, in the sentence you were thinking of:

「広さは５０００m²以上です。」

「５０００m²以上」 functions as a noun.

Answer 2

In this sentence there is no difference in meaning between です and あります. But あります sounds politer.