OSPF preferred route using cost

Looking for help on prefering OSPF routes from one datacentre over another - without having adverse affects.

I have 2 datacentres and 1 office that all have ipsec tunnel interfaces between them - full mesh

DC1 = 10.10.0.0/16

DC2 = 10.20.0.0/16

OFF1 = 10.40.0.0/16

Both DCs have direct connectivity to another DC3 = 10.30.0.0/16 - and will receive OSPF routes from it.

OFF1 does not have direct connectivtiy to DC3.

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From OFF1 I want traffic destined for DC3 to route through DC1.

So I could put a high ospf cost on the tunnel interface from OFF1 to DC2 and make it less preferable.

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My concern is that DC2's 'own' network of 10.20.0.0/16 will be less preferable and OFF1 will route traffic to DC2 through DC1 - which would be suboptimal.

I've simplified things here - in reality i have 5 datacentres and 20 offices - not a massive WAN !

Any help much appreciated.