Just remember this, a transformer is designed for a purpose and it can be either a step up transformer or a step down transformer. Everything else you need to know is here.
Go to this web site to pick up the basic theory:
formatting link
Go to this link to understand that it will work:
formatting link
Go to this link for the formula an equations required to design and build your own:
Notes for an Introductory Course On Electrical Machines and Drives
formatting link