An example of dynamically generated strong properties for Umbraco ModelsBuilder

SmartPropertyType.cs

//A PublishEventHandler catches the DataTypeService.Saved method as a developer workflow entry point;
//When the data type is saved this kicks off the generation and writes a model to our models folder
//This could be app_code if you don't use VS to build your solution, but we generate our ModelsBuilder models 
//into a class which is then built as part of the solution

 internal class PublishEventHandler : ApplicationEventHandler
 {
        public const string FileSuffix = ".smartpropertytype.cs";

        protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            DataTypeService.Saved += DataTypeService_Saved;
        }

        private void DataTypeService_Saved(IDataTypeService sender, global::Umbraco.Core.Events.SaveEventArgs<global::Umbraco.Core.Models.IDataTypeDefinition> e)
        {
            if (e.SavedEntities.Any(entity => entity.PropertyEditorAlias == "CONTROLALIAS" || entity.PropertyEditorAlias == "OTHERCONTROL"))
            {
                //GENERATE THE MODEL FILE (OVERWRITE .CS IF EXISTS) 
            }
        }
}

//Our config for ModelsBuilder
/*
    <add key="Umbraco.ModelsBuilder.Enable" value="true" />
    <add key="Umbraco.ModelsBuilder.ModelsMode" value="AppData" />
    <add key="Umbraco.ModelsBuilder.ModelsNamespace" value="Project.ContentModels" />
    <add key="Umbraco.ModelsBuilder.LanguageVersion" value="CSharp6" />
    <add key="Umbraco.ModelsBuilder.ModelsDirectory" value="~/../Project.ContentModels/Generated" />
    <add key="Umbraco.ModelsBuilder.AcceptUnsafeModelsDirectory" value="true" />
*/


//The normal Umbraco ModelsBuilder generates models like this, so we don't and can't alter this behaviour
//So we let ModelsBuilder generate its own models and write them
//Here is a sample of a minified generated model for homepage, this should be familiar if you've used ModelsBuilder

namespace Project.ContentModels
{
	/// <summary>Homepage</summary>
	[PublishedContentModel("homepage")]
	public partial class Homepage : PublishedContentModel, IPageHeader
	{
	#pragma warning disable 0109 // new is redundant
		public new const string ModelTypeAlias = "homepage";
		public new const PublishedItemType ModelItemType = PublishedItemType.Content;
	#pragma warning restore 0109

		public Homepage(IPublishedContent content)
			: base(content)
		{ }

	#pragma warning disable 0109 // new is redundant
		public new static PublishedContentType GetModelContentType()
		{
			return PublishedContentType.Get(ModelItemType, ModelTypeAlias);
		}
	#pragma warning restore 0109

		public static PublishedPropertyType GetModelPropertyType<TValue>(Expression<Func<Homepage, TValue>> selector)
		{
			return PublishedContentModelUtility.GetModelPropertyType(GetModelContentType(), selector);
		}

		///<summary>
		/// Content
		///</summary>
		[ImplementPropertyType("propertyAlias")]
		public IHtmlString PropertyAlias
		{
			get { return this.GetPropertyValue<IHtmlString>("propertyAlias"); }
		}
	}
}

//As a developer, when you are editing a data type which represents something you want a custom model for
//e.g. when you would normally generate a dynamic or jObject property but would really prefer a strong class
//you go and save the data type, then the event is caught by the handler above and this generates an additional model class 
//file for your custom content
//Here's an example of one of those (faked for this gist)
public class StrongJsonDeserializedModel
{
  public StrongJsonDeserializedModel(string json)
	{
		var that = JsonConvert.DeserializeObject<StrongJsonDeserializedModel>(json);
		this.X = that.X;
		this.Y = that.Y;
	}
	public int X {get;set;}
	public int Y {get;set;}
}

//This is an additional Homepage partial class that is also generated by our datatype save event
//it implements the property propetyAlias 
//https://our.umbraco.org/Documentation/reference/templating/Modelsbuilder/Control-Generation#implement-property-type
//As per Indicates that a property implements a property type with a given alias. The attribute must decorate the
//corresponding property type property. Use when alias and property name do not match.
//This will cause the property propertyAlias to not be generated, since you already implement it as StrongPropertyAlias.

public partial class Homepage
{ 
  [ImplementPropertyType("propertyAlias")]
  public StrongJsonDeserializedModel StrongPropertyAlias { get { return new StrongJsonDeserializedModel(this.GetPropertyValue<string>("propertyAlias")); } }
}

//now from your view:
@inherits Umbraco.Web.Mvc.UmbracoTemplatePage<Homepage>
@{
	Layout = "Master.cshtml";
}
//@Model.Content.StrongPropertyAlias => StrongJsonDeserializedModel
@Model.Content.StrongPropertyAlias.X