Having new turf can make a huge difference to your lawned area. New turf needs to be looked after in order to ensure that it grows and maintains it luscious green colour. You need to think about the area that you are going to be laying the turf down in before you place an order for turf. Sometimes, if the soil is good under you can just lay the turf on top but if they soil is of poor quality or has been neglected for a while then you may want to consider adding a layer of topsoil. Grass plants need at least 15cm of good quality, well prepared topsoil to root into, so if you do not have this, you will need to purchase topsoil. Most turfing companies will also provide topsoil. This will of course add to the cost of the turf but there is no point in spending a lot of money on turf if the soil underneath is so poor it means that the turf is not going to take and will eventually die.
If you are unsure as to whether you need topsoil then you may be able to ask a gardener, landscaper or the turfing company for their advice.