Docker File - Skipping Project. Because it was not found

In my case the project file was not found because i was building a linux container, and for some reason, the project filename and it's path had different letter case then in the filesystem.

Based on your input I propose below folder structure and Dockerfile.

[Solution] 'BuySellApi' (3 Projects)
  |
  +-- Dockerfile
  | 
  +-- [BuySellApi]
  |    |
  |    +--- BuySellApi.csproj
  |
  +-- [BuySellApi.Core]
  |    |
  |    +--- BuySellApi.Core.csproj
  |
  +-- [BuySellApi.Data]
       |
       +--- BuySellApi.Data.csproj

Dockerfile

    FROM microsoft/dotnet:2.2-aspnetcore-runtime AS base
    WORKDIR /app
    EXPOSE 5000
    ENV ASPNETCORE_URLS=http://+:5000

    FROM microsoft/dotnet:2.2-sdk AS build
    WORKDIR /src
    COPY . .
    RUN dotnet restore ". BuySellApi/BuySellApi.csproj"
    WORKDIR "/src/BuySellApi"
    RUN dotnet build "BuySellApi.csproj" -c Release -o /app

    FROM build AS publish
    WORKDIR "/src/BuySellApi"
    RUN dotnet publish "BuySellApi.csproj" -c Release -o /app

    FROM base AS final
    WORKDIR /app
    COPY --from=publish /app .
    ENTRYPOINT ["dotnet", "BuySellApi.dll", "--server.urls", "http://0.0.0.0:5000"]

As suggested by @Mihai

I moved my Dockerfile directly under solution file and made some changes to it as below:

FROM microsoft/dotnet:2.2-aspnetcore-runtime AS base
WORKDIR /app
EXPOSE 5000
ENV ASPNETCORE_URLS=http://+:5000

FROM microsoft/dotnet:2.2-sdk AS build
WORKDIR /src
COPY ["BuySellApi/BuySellApi.csproj", "BuySellApi/"]
COPY ["BuySellApi.Core/BuySellApi.Core.csproj", "BuySellApi.Core/"]
COPY ["BuySellApi.Data/BuySellApi.Data.csproj", "BuySellApi.Data/"]
RUN dotnet restore "BuySellApi/BuySellApi.csproj"
COPY . .
WORKDIR "/src/BuySellApi"
RUN dotnet build "BuySellApi.csproj" -c Release -o /app

FROM build AS publish
RUN dotnet publish "BuySellApi.csproj" -c Release -o /app

FROM base AS final
WORKDIR /app
COPY --from=publish /app .
ENTRYPOINT ["dotnet", "BuySellApi.dll", "--server.urls", "http://0.0.0.0:5000"]