I'll assume you are trying to make an annotation family, these instructions are for if you started with a generic annotation template:
1. Make a new General Annotation Family.
2. Change Family Category if desired (Settings, Family Categories and Parameters)
3. Draw your arrow using lines.
4. Draw a reference line from the desired center of the arrow to the past back of the arrow .
5. Drag the part of the Reference line that you drew past the back of the arrow back to the intersection of it and the arrow. When the lock symbol appears, lock it.
5. Group the reference line and the lines of the arrow together.
6. Move the group, putting the endpoint of the ref line (at the center of the arrow) to the intersection of the two default planes in the template file.
7. Make a dimension from the left side of the horizontal line to the ref line in the arrow group.
8. Make a new angle instance parameter named "Angle" (or whatever you want). Type in 45 degrees.
9. Select the angular dimension, then change the Label to the parameter you just made.
Play around with the family dimension to see if it works. You'll also need to add your text, which you simply center align and place on the center of the arrow.
Let me know if you have any problems.
PS..I know how frustrating this is....I had to figure it out to have a North Arrow with the angle parameter on my title sheet. Though I would be interested to hear of another way.
**Using Revit Architecture 2009, 2011, and 2012**