I think you should use 'outside' rather than below. If you lived in a flat or apartment within the building: "I am outside your flat, come down" If you lived in a house: "I am outside your house, come outside"

I think that instead you should say "I'm near your house, come down." or "I'm by your house, come down." Saying "below" would mean that you're under his house. Saying "near" or "by" would mean that you're close to his/her house.

"I'm right below you, come on down!" Or... "I'm right below your place, come on down!"