How to add self made side objects.

m working on the road tool and wants to add side objects that i hv made.wat do i hv to do for dat ,i hv already seen the video about this,bt wat i want to knw is dat is there any specification for creating the object,i mean to say its placement should be on origin or it can be placed anywhere we want.m asking this cauz i hv created the prefab for my side objects and they are visible if i dropt them individually into the scene bt as soon as i click on BUILD THE SIDE OBJECT button ,nothing happens and i m stuck here for the last 2 days and dnt knw wat exactly is the issue.i hc done exactly wat the video shows bt dnt knw where m going wrong