I'd propose to add the items to the existing CodeCommentStatementCollection
instead of creating a new one:
CodeCommentStatement[] documentation = { docStart, docContent, docEnd}
property.Comments.AddRange(documentation);
The collection provides the common methods for adding: Add, AddRange for an array, AddRange for a CodeCommentStatementCollection.
As pointed out by @svick in the comments, you can also assign the value when instantiating the object, e.g.
var property = new CodeMemberProperty {
// Other initialization values
Comments = { docStart, docContent, docEnd } }
In case you wonder why and how this works on a readonly property, see this question and its answer.