A good place to begin is the Library's Archicture Research Guide (under "Research by Subject" on the Library home page) to get help finding plans. Use the tab at the top of this Guide called "Drawing & Plans". Be sure to add the term "plans" to your searches. Often books provide high resolution plans and elevations, so you may want to start your search in the Library catalog.
Also, listed on the Architecture Research Guide Drawings & Plans tab is the Avery Index where you can search for articles from architecture periodicals. Once at Avery, you can go to the "Advanced Search" feature and limit by choosing "plans" and/or "sections" under "Physical Description" to find only articles with plans and/or sections. Some of these may be in paper format only and you will have to request Library staff to retrieve the journal for you. Be sure to get all of the information about the article to allow us to find it such as the title of the journal, title of the article, the year and month it came out, and any volume number information.
If you still are not finding what you need, be sure to ask a librarian to assist you.