You can use the WSDL w/SoapUI to create builds http://www.inflectra.com/SpiraDemo3/Services/v4_0/ImportExport.aspx?
or if you have a supported version control provider, you can integrate it with SpiraTeam (not sure about SpiraTest) and automatically create builds when code is pushed out. Check out the documentation section and in Spira unser "Administration -> Integration -> Version Control".
We use SoapUI, because we have three sources of code and they are not all from within our firewall.