No, you cannot draw up your own.
Here's a good source for information about DH contracts.
http://www.immd.gov.hk/ehtml/hkvisas_5.5.htm
Best to hire an employment agency as they local consulates need the contracts to originate from an agency (rather bizzare nexus ... ).
Check with the Singaporean agencies, depending on the nationality of your helper they may be able to work something out for you. The local agencies in HK do not want to deal with Indonesian helpers directly hired by employers as they cannot extract "fees" from the helper (which is illegal anyways)