There are some trees outside of the building.
There are some trees outside the building.
Are they both correct?
I think the second sentence is correct:

There are some trees outside the building

As far as I know, "outside" doesn't need the preposition "of" after it.

Hope this helps
Thanks for your reply
Actually,I've just found a sentence in a dictionary which is (They live in a little town outside of Reed City.
How about this?
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Oooops, sorry salam1101. Maybe you are right there.
I researched a little and this is what I found:

From cambridge.org:
"Outside of"-----> (mainly US) "except for".
Outside of us three, no one knows anything about the problem, yet.

But, now I have a doubt about the usage of "outside of" in your sentence. I would always say "outside Reed City". I haven't got the rest of my grammar books with me so I can't look it up right now. Let's see if someone else can give us a little help here.
Emotion: tongue tied
Novalee ,Thanks anyway
May be I can have some comments from Miriam if she is not busy.
Hello, Salam and Novalee. Emotion: smile

Andrei asked about the use of "outside" and "outside of" a while ago. Here's the url to the thread, in case you wish to have a look at it:

Basically, it seems both are accepted.

Hope it helps.

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Rather than having to cut and paste, here is the [url="http://www.EnglishForward.com/ShowPost.aspx?PostID=34229 "]link[/url] that Miriam was referring to.