You can request copies of plans - the request will in all probability be refused!
Why would a house builder hand over copies of his working drawings and designs to a customer?
It should be obvious that most customers in possession of plans would then check their house for any deviation from the plans.
If any are found, require the builder to take action, which he would otherwise have avoided.
Further, such plans belong to the builder and are his intellectual property.
You could offer to buy the plans you require which the builder may agree to subject to conditions.
Finally, taking a photo of the plans is unlikely to be permitted for the reasons above.
However, quite often plans are revised due to charges to regulations and standards with the out of date plans dumped in rubbish skips.
Sometimes plans may be left by trades in part-finished homes if you can legally gain access.
Another option would be to give a worker on the site a "drink" for the particular plan you would like.