Coding an accounting database from scratch?
I have used almost all accounting software, currently use and modify Sql-Ledger - and so turning my database client's workflow system into a full, double-entry accounting system was so easy it was almost a relief; client had been using my system to bill their own (news-copy) clients because their internal itemisation of services spoke their own language whereas no accounting package would. Their accounts section then had to go and reproduce it all again externally for book keeping.

Finally the client's accountant and I sat down and exchanged notes. I modified the application within a week. It has never broken, produced a bug, or failed. It does all their accounts and no none else's. It tracks assets, cash flow, everything except payroll - which they didn't need.

Every business of any size knows, you just can't get anything off the shelf that works. 

My advice is don't listen to the doom-and-gloom advice of anybody who doesn't understand both database schema and accounting. This combination seems to be just unusual enough to have software vendors rubbing their hands with glee, issuing warnings of dire consequences to would-be developers, spending most of their time organising vendor-lockin components to their software, or arrangements with large accounting franchises. And, like successful snake-oil vendors, they laugh all the way to the bank.