i make sweet potato pies all the time but have never made one with a top on it
what i need to know is , is it best to use a lattice top or a complete top and does the cooking time increase

I have never tried this either, but if I did, I’d try a lattice top so some of the steam can evaporate from the filling while baking. Also, the crust may soak up moisture from the filling so plan to eat it fairly soon after baking/cooling.

I think Barbara is on the right track, sweet potato pie is very wet.  How about cutting out extra crust in decorative shapes and bake them separately on a cookie sheet, then place them on each slice just before service (fall leaves, acorns, etc).