public interface IWebRequestFactory
{
    HttpWebRequest Create(string url);
}

public interface IVKLikeService
{
    void Like(tring userId, VkPhoto vkPhoto, bool like);
}

public interface IRequestBuilder
{
    IRequestBuilder Param(string key, string value);
    IRequestBuilder Url(string url);
    IRequestBuilder Method(HttpMethod method);
    HttpWebResponse Execute();
}

public class RequestBuilder : IRequestBuilder
{
    private string url;
    private HttpMethod method;
    private IDictionary<string, string> parameters = new Dictionary<string, string>();

    private IWebRequestFactory webRequestFactory;

    public BaseRequestBuilder(IWebRequestFactory webRequestFactory)
    {
        this.webRequestFactory = webRequestFactory;
    }

    private void ApplyDefaultHeaders(HttpWebRequest request) {...}

    private void WriteParams(HttpWebRequest request)
    {
        using (var writer = new StreamWriter(request.GetRequestStream()))
        {
            writer.Write(CreateParamsString());
        }
    }

    private string CreateParamsString()
    {
        var builder = new StringBuilder()
        ...
        return builder.ToString();
    }

    public IRequestBuilder Param(string key, string value) {...; return this;}
    public IRequestBuilder Url(string url) {...; return this;}
    public IRequestBuilder Method(HttpMethod method) {...; return this;}

    public HttpWebResponse Execute()
    {
        var request = webRequestFactory.Create(url);

        ApplyDefaultHeaders(request);
        WriteParams(request);

        return request.GetResponse();
    }

}

public class LikeRequestHelper
{
    private IRequestBuilder builder;

    public LikeRequestHelper(IRequestBuilder builder)
    {
        this.builder = builder;
    }

    private string GetObjectString(string userId, VkPhoto vkPhoto)
    {
        return $"photo{userID}_{vkPhoto.id}";
    }

    public IRequestBuilder Build(string userId, VkPhoto vkPhoto, bool like)
    {
        var act = like ? "a_do_like" : "a_do_unlike";

        return builder
            .Url(VKApi.Like)
            .Method(HttpMethod.Post)
            .Param("act", act)
            .Param("object", GetObjectString(userID, vkPhoto))
            ....
            .Param("hash", vkPhoto.hash);
    }
}

public static class RequestBuilderExt
{
    public static IRequestBuilder BuildLikeRequest(this IRequestBuilder builder, string userId, VkPhoto vkPhoto, bool like)
    {
        var helper = new LikeRequestHelper(builder);
        return helper.Build(userId, vkPhoto, like);
    }
}

public class VKLikeService : IVKLikeService
{
    private IWebRequestFactory webRequestFactory;

    public VKLikeService (IWebRequestFactory webRequestFactory)
    {
        this.webRequestFactory = webRequestFactory;
    }

    public void Like(string userId, VkPhoto vkPhoto, bool like)
    {
        var builder = new RequestBuilder(webRequestFactory);
        builder.BuildLikeRequest(userId, vkPhoto, like).Execute();
    }
}