Collar Ties that connect rafters below the ridge in the top third of the roof frame as required at a maximum 4' spacing are missing on the frame of this home as seen thru the attic access. Collar Ties prevent rafter uplift and separation, that can cause structural issues. Collar Ties are required to be at least 1x4"(nominal) material but are most commonly at least 2x4's. This is on a conventional stick frame (non truss) structure, as engineered trusses do not require collar ties from a framing material as they are tied together with metal plates / gussets. 
Visit our blog on collar ties, rafter ties of the roof frame for more info.
Also, there is apparent moisture issues, penetrations in this attic as noted from the dark areas of the roof decking in the photo above, as further evidenced with the moisture stains and roof decking patches/ repairs as seen in the picture below of the same attic.

For more roof framing information, click below:
http://www.jwkhomeinspections.com/blog/collar-ties-rafter-ties-purlins-san-antonio-home-inspector.html

Photos by San Antonio Home Inspector Joe Keresztury, JWK Inspections