Lots of people DIY. Where are you based? Just make sure that you are likely to get admission to you preferred school based on distance (DCs have to achieve a score of 121+ and then it is entirely down to distance in Bucks). Berkshire is different.
You might be better looking in the regional sections. I'm not familiar with Berks, but information about the Bucks test is here:
https://www.elevenplusexams.co.uk/schoo ... re-11-plusThere is a similar pages for Berkshire. Also, this thread should help for Bucks:
viewtopic.php?f=12&t=53382