Hello @Jeank and welcome to our wonderful community. I am very sorry you don't have the build a bot. I find it a very useful event to have. Unfortunately some people do not have it. The studio is always looking for ways to make the game more interesting and challenging and sometimes that means randomly chosen groups of people get (or don't get) access to certain events. The good news is that this is usually for a limited amount of time (but could last 4-6 weeks or possibly longer).
In the meantime - in case that is not the reason why you don't have it please ensure you have the latest version of the app, that you have cleared your cache and then restart the platform you are playing on (mobile or PC). If that hasn't brought the build a bot into your game - then please be patient and hopefully he will return soon. You might also start a discussion thread or look for one already in existence, to share you opinion about not having access to the build a bot.