Very hard question to answer with out more details on your house. What type of house is it? Are you simply rearranging partitions or adding on to the existing? How many bedrooms do you currentely have?
With out those as a general rule a Master Suite will add value to your home. Depending on the size and materials used you can expect between 50-75% of the cost to be recoup'd. Having it on the first floor is a matter of taste in my opinion, most people I think prefer the bedrooms on the second, me personaly I like a 1st floor master its eaiser to sneak to the kitchen for a cookie with out waking the kids!