Builder base class in #csharp

BuilderBase.cs

using System;
using System.Threading.Tasks;

namespace FooBar
{
    public interface IBuilder { }

    public interface IBuilder<TBuildResult, TBuilder> : IBuilder
        where TBuildResult : class, new()
        where TBuilder : class, IBuilder
    {
        TBuildResult Build();

        TBuilder With(Action<TBuildResult> setAction);

        TBuilder With<TRequestBuilder>(Action<TBuildResult, TRequestBuilder> setAction) where TRequestBuilder : class, IBuilder, new();
    }

    public class BuilderBase<TBuildResult, TBuilder> : IBuilder<TBuildResult, TBuilder>
            where TBuildResult : class, new()
            where TBuilder : class, IBuilder
    {
        protected TBuildResult obj = default(TBuildResult);

        public virtual TBuildResult Build()
        {
            var inst = obj.GetType().GetMethod("MemberwiseClone", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
            return inst?.Invoke(obj, null) as TBuildResult;
        }

        public TBuilder With(Action<TBuildResult> setAction)
        {
            setAction?.Invoke(obj);
            return this as TBuilder;
        }

        public async Task<TBuilder> With(Func<TBuildResult, Task> setAction)
        {
            await setAction?.Invoke(obj);
            return this as TBuilder;
        }

        public TBuilder With<TRequestBuilder>(Action<TBuildResult, TRequestBuilder> setAction)
            where TRequestBuilder : class, IBuilder, new()
        {
            setAction?.Invoke(obj, new TRequestBuilder());
            return this as TBuilder;
        }

        public async Task<TBuilder> With<TRequestBuilder>(Func<TBuildResult, TRequestBuilder, Task> setAction)
            where TRequestBuilder : class, IBuilder, new()
        {
            await setAction?.Invoke(obj, new TRequestBuilder());
            return this as TBuilder;
        }

        public static implicit operator TBuildResult(BuilderBase<TBuildResult, TBuilder> builder) 
            => builder.Build();
    }
}