for what purpose are interested?
a question of statistics?
or the question is asked with the purpose to choose the right iron for yourself?
If the statistics then:
buildserver — virtual car hastasana on xeon 3.4 GHz memory 508 Mb. Wheelbarrows on this server spin 8 pieces, do not know... operating system 2008 R2. So a server is not particularly fast.
If the question of choice, it is necessary to know the tasks that need to run the server. on Average, the criterion should be: Time from beginning of Assembly to the moment when it will be possible to give an answer to the question "Ready to build manual testing" should not exceed 10 minutes. Although this rule applies only in cases of continuous integration.