newly levelled garden with heavy clay soil base

betagarden

We are in the middle of a big extension/garden project. The garden used to be in three different levels and it has taken 20 grab lorry to get them in one reasonable flat level.

We have spent too much money to get the garden in one level and will not have enough money to bring in professional gardeners to do the turf. The garden work has already eaten into our budget for the extension work. 

Initially we planned to get a lorry of topsoil in and lay the topsoil ourself then do the turf. The problem is we have very heavy clay type of soil in the garden (as the grass and all nice topsoil in the three levels have all been removed to create one flat level I wish I could save some of that for now, but there weren't any space). Can we simply just lay 2 inches of topsoil on top of this compacted hard clay soil? Will we have drainage problem and end up with mosses in future? Do we need to mix some sandy topsoil with the clay base and then do a layer of topsoil on top of that? 

(Or should we give up and get professionals to look at this, not sure where we can find more money though.....)

any advice would be appreciated. Thanks.