## How to find a basis for the space of cusp form of congruence subgroups

In fact, I just want to find the basis for cusp form of $/Gamma_0(N)$.
And I have done for several cases such as N=5 , weight=4 by Dedekind Eta function.
But in some cases I can not find a spenning set such as N=5, weight=8.
Is there a better method to find the basis??