User Rights - Can alter Sp's but not tables
I presume your users are creating reports or data extracts.  You can grant permissions to a particular schema, so you could create a separate schema for your users and have the stored procedures reside in that schema.  Configure the security on the rest of the objects so the users only have read permission.

You can also do something similar by creating a separate database and either require explicit reference to the tables or create synonyms within the reporting DB.