<apex:page standardController="CustomObject__c" extensions="CustomObjectCtrlExt" >

    <apex:form>

        <apex:pageBlock>

            <apex:pageBlockButtons >
                <apex:commandButton value="Save" action="{!save}"/>
                <apex:commandButton value="Cancel" action="{!cancel}"/>
            </apex:pageBlockButtons>

            <!-- Record Type 1 -->
            <apex:pageBlockSection rendered="{!recordtypename == 'RecordTypeName1'}" >
                ...
            </apex:pageBlockSection>


            <!-- Record Type 2 -->
            <apex:pageBlockSection rendered="{!recordtypename == 'RecordTypeName2'}" >
                ...
            </apex:pageBlockSection>


            <!-- Record Type 3 -->
            <apex:pageBlockSection rendered="{!recordtypename == 'RecordTypeName3}" >
                ...
            </apex:pageBlockSection>



            ...



    </apex:form>

</apex:page>