Sample request information to create metadata using SFDC REST APIs

MetadataCreation.txt

Headers - Authorization: OAuth <YOUR_SESSION_ID>
Content-Type: text/xml
SOAPAction: createMetadata

URL - /services/Soap/m/35.0

Body -
<?xml version="1.0" encoding="UTF-8"?>
<env:Envelope
    xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <env:Header>
        <SessionHeader
            xmlns="http://soap.sforce.com/2006/04/metadata">
            <sessionId>YOUR_SESSION_ID</sessionId>
        </SessionHeader>
    </env:Header>
    <env:Body>
        <createMetadata
            xmlns="http://soap.sforce.com/2006/04/metadata">
            <metadata xsi:type="CustomObject">
                <fullName>MyCustomObject2__c</fullName>
                <label>MyCustomObject2</label>
                <pluralLabel>MyCustomObject2</pluralLabel>
                <deploymentStatus>Deployed</deploymentStatus>
                <sharingModel>ReadWrite</sharingModel>
                <nameField>
                    <label>ID</label>
                    <type>AutoNumber</type>
                </nameField>
            </metadata>
        </createMetadata>
    </env:Body>
</env:Envelope>