Ext means externalNah, it asks for a whole lot more measurements than that.
It lost me on the question of - No. ext walls length-wise and then again width-wise???
If you have a detached house you will have two external walls width-wise and two length-wise.
If you have a semi-detached or end terrace, you will have two width-wise and one length-wise.
If you are mid terrace, you will have two width-wise and none length-wise.
If you need any more help, just ask.