I, of course, had my husband build a custom frame because I can't leave well enough alone.
Felt Letter Board Tips And Tricks - I need to revisit this post by Love and Renovations
Here are some links to some DIY versions of Letterboards. I haven't tried either of these DIY's but they look totally plausible and not in the pinterest fail realm.
DIY Letter Board (treasures and travels blog)
Vintage Letterboard DIY (settling in sawdust blog)
link to the whole series
check out Write31Days