You may want to complete your hour building when you complete your ATPL theory, as you need to have 100PIC (and 150TT) before you can start your CPL/IR courses. This is because you only have 36 months from passing your last ATPL exam to complete the CPL/IR in order to gain a Frozen ATPL or you will have to resit your ATPL theory exams again.
This is if like me, money for flying only comes in slowly. I intend to have hour building done and paid of at the same time as I complete my ATPL theory. And then I can start off new fresh debts.
good luck
mint