I would avoid at all costs due to the following
1, they want it cheap, they will want you to fit cheap ■■■■■ parts that will fail and it will be your fault
2, they wont want to pay you straight away, a few will not pay you ever!
3, they will want 30 days credit (bigger boys 60 days) incl parts and parts can soon get into serious money
4, you need to have some heavy/expensive/easily nickable kit
5, if you have no diagnostics kit you are on the back foot straight away, the generic diag tools like Texa are just utter carp
6, did I mention 2 
Any half tidy hgv mechanic paperwork or not can earn 750 a week with little hassle and nearer a 1000 if hes keen.