You can build muscle on paleo.
How you go about it depends on whether you are trying to gain weight or merely to recomposition to decrease fat at the same time.
In either case you will need to be eating a protein surplus and doing strength training.
If you are trying to recomposition, you would maintain your weight by eating just enough calories to do that, which will depend on your metabolism and your exercise. If you are a naturally skinny, you may have to eat a lot of extra calories to gain that weight.