Question about completing items vs buying many parts

Okay so I'm going to use some of my recent Vladimir experience as an example. Lets say I was going against an AD top lane, but their mid lane AP is getting fed, and they have strong AP as support as well. As , getting my is generally first and formost, but after that I'll build a for defense against my opponent. Now, before I could ever finish that armguard into a , the team starts to group and I find myself taking a lot of AP damage, so I would like some MR in the form of or .

Am I hurting myself by delaying so many finished items? Running around with my inv looking like