Custom monster creation new user question

[bearjew]

I recently got HL and am getting acquainted with it. While making the first few encounters, I realized that some of the creatures aren't in the base pack that I have. I've looked around and it seems as though I should be able to create a custom monster without having to buy the bestiary packs, but I'm having a bit of trouble doing this (I've looked on youtube as well and some of the interface options they have are quite a bit different). I'm trying to build the Giant Bombardier Beetle from the Crypt of the Everflame module.

In the "Configure Your Hero" window that opens, I'm choosing NPC and then pick/roll ability scores, followed by choosing it to be an enemy of the party. However, I dont have the ability to choose a Custom Monster in my Race choice window. I can check all the boxes in the "customize" window, except the "customize special race abilities" because I dont have the bestiary package - but I'm not sure that I really need to be able to use that option at the moment. I also can't seem to input a (-) Ability Score, but only a 0 and I'm not sure if this makes a difference but it seems to. Am I going about this correctly? Any help would be greatly appreciated.

Thanks!