Does roblox gives you a virus

No, it does not give you viruses. The site is completely safe, and many anti-virus softwares have tested this site, and said that it does not have any.
However, the Advertisements can if you click on them, and a FEW (note: few) of the downloadable skins can. If you want a skin, make sure you scan your computer right after, with a good antivirus program (AVG is a good one)

None of the levels are any threat, and none of the downloadable content represented by the site itself will have any.
If you don't think my answer is relevant or correct, go ahead and check anywhere else. about 95% of the answers (what i've seen at least) agree.