The deluxe rooms are furnished in a very simple and spacious style or The deluxe rooms have been furnished in a very simple and spacious style.
One is a present tense form of the verb "to be", the other one is the present perfect progressive tense. They both denote pretty much the same thing in those sentences.
@qwikad.com is correct in that both are proper grammar and syntax. However, I think that the present tense is more effective in copywriting, in most cases. Simpler construction is usually better.
Since you did not give us enough information, there is NO way that we can tell you whether they are true or not. What we can tell you is that if they are refering to the SAME rooms at the SAME time, the statements are either both true OR both false. In such a situation, one CANNOT be true while the other is false.
You can't describe a style as "spacious", at least not in my point of view. Apart from that, they are pretty much the same. I would go with "The deluxe rooms are furnished in a very simple and spacious style", it gives the impression that they are newly furnished, while the other sentence may create the feeling that the furniture is older.
Both are not perfect but if you wanna put this content on a website then I recommend you to go with first one.