hi

yes but you only have to put one iwad

1. just go to your files

2 .go to my local disk

3. go to program files (x86)

4. go to steam

5. go to steamapps

6. then to common

7. then find doom (it could be ultimate doom or doom 2 ect.)

8. click on the doom file and you will see ''Base'' click on it and you should see doom 2 or doom wad

9. copy it and go to your garrys mod folder and paste it in you garrys mod folder

i will tell you how to get to your garrys mod folder

1. go to files

2. then to local disk

3. go to program files (x86)

4. to steam

5. then to steamapps

6. then to common

7. go to garrys mod and then you're there

i hope this helped you and wasn't too confusing if you need help just comment in this discussion and eventually i will reply