That's fine, but what help do you want?
Lots of things need to be answered:
Isolation of primary to secondary;
EMC regulations to be complied with;
Environmental requirements commercial/industrial/military/automotive?
Size, weight;
Target efficiency if this is an issue;
Type of control or man/machine interface: Manual, computer links - RS232 or Internet or what;
Transient performance;
Target cost;
Likely manufacturing quantities 1, 10, 100s or large;
Likely location of manufacture and availability of plant and equipment and labour;
Level of automation available to assist design and/or manufacture;
Why not just buy one?