So I have done the drawbridge in GTA IV but this is how you work it otherwise you won't be able to get to
the house. 
Step 1.) Go into Map Editor
Step 2.) You can see the gates laters foot and now press so you see it or go to current objects
Step 3.) Copy it and check off Dynamic tick box
Step 4.) Pull up to the edge of the box and you will drive across it

If you need help just contact me. 
Skype: deviantamazed
Twitter: deviantamazed
YouTube: deviantamazed


NOTE: You may need to clear the map then load it again for everything to spawn. 

Other of my mods
https://www.gta5-mods.com/users/Avery