I don't have SiteBuilder, but...if you can get into the form_editor.tpl via your ACP, then look for the lines near the bottom that start with "plugins:" and "toolbar1".
Here are some snippets that I have added to add more options to the font styling, and some other features buttons I (rather inelegantly) added to my text editor:
plugins: "contextmenu,pagebreak,{if $jrsmiley}jrsmiley,{/if}{if $jrembed}jrembed,media{/if},image,autoresize,{if $table}table,{/if}link,code,fullscreen,textcolor,colorpicker,preview{if $hr},hr{/if}",
toolbar1: "formatselect | fontselect fontsizeselect forecolor {if $strong} bold{/if}{if $em} italic{/if}{if $span} underline{/if} | {if $span || $div} alignleft{/if}{if $span || $div} aligncenter{/if}{if $span || $div} alignright{/if}{if $span || $div} alignjustify |{/if}{if $ul && $li} bullist numlist |{/if}{if $div} outdent indent |{/if} undo redo | link unlink anchor pagebreak{if $table} table{/if}{if $hr} hr{/if} | code preview fullscreen{if $jrembed || $jrsmiley} |{/if}{if $jrembed} jrembed{/if}{if $jrsmiley} jrsmiley{/if}",
-pay particular attention to the toolbar1 line where I have added:
"fontselect fontsizeselect forecolor"
add the above missing wording in where I have it in the toolbar1 line, and save changes. Be sure to check the checkbox to activate the change. See if it works ok for you, if not just click to reset the template the way it was before.
Note- I'm not sure that's going to set the "default font/size for the site" as you seem to be angling for in this thread though. But it may add the font options in the text editor that you are wanting.
--
...just another satisfied Jamroom customer.
Migrated from Ning to Jamroom June 2015
updated by @strumelia: 02/23/16 03:19:33PM