This question comes up very often and in fact I just got one. A blogger tries to get the blogspot.com URL he wanted, but someone has already taken it but has not updated it for long time or may even not have made any post at all. Question is, can he have the URL? Short answer at the bottom of post, in red.
1. According to Blogger policy, blogspot URL do not expire. That means theoretically, they are forever. However, if it has been identified (rightly or wrongly) as a spam blog, there is a possibility that the blog will be deleted and the URL becomes available again and then you can have your go for the URL.
2. According to Gmail policy, if there is no activity on your Gmail account for 9 months or more, your Gmail address can be deleted. If you use that Gmail address as the username for a Blogger account, and it has been deleted, it is likely that the same may happen to your Google account together with the blogs (this may also apply to the blogger whose URL you want).
Amazon products for Blogger
But what if the Blogger account is started with a non-Gmail email address like, for example, Yahoo?
Yahoo, when it first started, says their email addresses are for life (what exactly "for life" is up to you/them to interprete). Now when you start a Yahoo email address, that message no longer appears, so I don't know what are their current policy is. However, if you don't sign into a Yahoo email address, it will be deactivated. I am guessing that if you use a Yahoo email address for your Blogger (Google), you have less chance of getting your Blogger (and Google) account getting deleted, together with the blogs.
I am testing what are the actual effects of all these mentioned at Will Blogger blogs ever be deleted?. The results wouldn't be known for some time.
So if you are eyeing a particular blogspot URL, if for any reason the blog is deleted, you can have a go at the URL.
Other possibility is to try to contact the blog creator and ask if he or she is willing to release it to you. Unfortunately, frequently, the profile in not made public, and even if it is made public, they may have chosen not to display their email address. In this case, you have no recourse.
But you have alternatives. You can become creative and alter the URL a little bit. For example,
is already taken (by me), but your can try
which may even be better because according to WebCEO, search engine cannot distinquish between words made into a compound word, but they can if you separate them using hyphen. This can be good for SEO (Search Engine Optimization) as the URL is given high weightage by search engines according to WebCEO. Further, if you jumble many words into a single compound word, you may end up with something that may convey a meaning very different from your original intention, some of which can be very embarrasing. You can find some funny examples in Webmasters who didn't think when they registered their URL.
Note that using hyphen in URL is controversial, and I am hoping to find the time to research the subject further. Also check the comments to read what Jan had to say about hyphen in URL
You can also try adding an extra word to an already taken URL. For example,
may be already taken, but you can try
If you are creative, there will always be a way around a problem.
BLOGGER WILL NOT HELP YOU GET A LONG UNUSED BLOGSPOT URL