Show your flexibility and your willingness to respect his/her time constraints. By setting the appointment up in a formal manner, it demonstrates your respect and professionalism.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
I plan to be in your area on <date> and wondered if it will be possible to meet with you. If it would be convenient, I could meet you <propose a location> <propose a time>.
I'll give you a call in the next few days to see what's most convenient for you. I look forward to seeing you.
encl: <List of enclosed items goes here>