SQL Server 2012 Express Report Services report builder button not visible
You can still install through ClickOnce deployment via (assuming you have configured SSRS with ReportServer as the installation path):

http://&lt;servername&gt;/reportserver/reportbuilder/ReportBuilder_3_0_0_0.application


It's still functional, but it's not full-featured.

Source

For example, Report Models are not supported and neither are ad-hoc queries through Report Models. This is an SSRS Express limitation which will manifest in Report Builder. Additionally, the language of the Supported Features of SSRS Express are somewhat ambiguous (nature of the English language) especially with regards to this line:


  Ad hoc reporting through semantic models and Report Builder is not supported.


What does the "and" connect and how does it connect them? Is it the clause "semantic models and Report Builder" or is Ad hoc reporting not supported through both semantic models and Report Builder. Unfortunately, the answer to this question could be more readily parsed at Linguistics.SE. But I digress. Suffice it to say, Report Builder is available to you in SSRS Express.