The workshop will be in the Aula Comitato, located near the Library of the research area. The IAPS building is U-shaped, you will see a couple of stairways leading downward in the middle of the U. When entering, you will find the library on the right, the Aula Comitato will be instead ahead of you slightly on the left.
For those staying overnight, if you are ok with using a taxi it is more advantageous to stay in Frascati: it is an old town on the hills just outside Rome and is actually nearer to the institute than the centre of Rome. It is a nice place to walk around and is full of restaurants.
Central Rome obviously offers a unique surrounding for an evening walk or if you want to extend your stay to the weekend, but the combination of metro and bus is very time consuming and is going to take you about 1 hour and a half to arrive to the Institute or go back to the hotel in the evening.
To arrive at the Institute from Frascati the most convenient option is the taxi.
To arrive to the Institute from Rome, you need to take the tube Metro A to Anagnina station (the final station eastward) and from there take the bus 509, which ends its run at the gate of the campus. Keep in mind the long travel times from the centre of Rome, though.